From 0b03b6a9ec5fc690796fa66d7a3b04e26cf8cece Mon Sep 17 00:00:00 2001
From: Simon Frei <freisim93@gmail.com>
Date: Fri, 11 Jan 2019 13:56:05 +0100
Subject: [PATCH] lib/model: Improve filesystem operations during tests (fixes
 #5422)

* lib/fs, lib/model: Improve filesystem operations during tests (fixes #5422)

Introduces MustFilesystem that panics on errors and should be used for operations
during testing which must never fail.
Create temporary directories outside of testdata.

* don't do a filesystem, just a wrapper around os for testing

* fix copyright
---
 lib/model/folder_recvonly_test.go   |  75 ++-----
 lib/model/folder_sendrecv_test.go   |  32 +--
 lib/model/model_test.go             | 325 +++++++++++++++++-----------
 lib/model/progressemitter_test.go   |   9 +-
 lib/model/requests_test.go          |  84 ++++---
 lib/model/sharedpullerstate_test.go |   9 +-
 lib/model/testos_test.go            |  82 +++++++
 7 files changed, 380 insertions(+), 236 deletions(-)
 create mode 100644 lib/model/testos_test.go

diff --git a/lib/model/folder_recvonly_test.go b/lib/model/folder_recvonly_test.go
index 1b73322be..286ad5727 100644
--- a/lib/model/folder_recvonly_test.go
+++ b/lib/model/folder_recvonly_test.go
@@ -22,29 +22,19 @@ import (
 )
 
 func TestRecvOnlyRevertDeletes(t *testing.T) {
+	testOs := &fatalOs{t}
+
 	// Make sure that we delete extraneous files and directories when we hit
 	// Revert.
 
-	if err := os.RemoveAll("_recvonly"); err != nil && !os.IsNotExist(err) {
-		t.Fatal(err)
-	}
-	defer func() {
-		if err := os.RemoveAll("_recvonly"); err != nil && !os.IsNotExist(err) {
-			t.Fatal(err)
-		}
-	}()
+	testOs.RemoveAll("_recvonly")
+	defer testOs.RemoveAll("_recvonly")
 
 	// Create some test data
 
-	if err := os.MkdirAll("_recvonly/.stfolder", 0755); err != nil {
-		t.Fatal(err)
-	}
-	if err := os.MkdirAll("_recvonly/ignDir", 0755); err != nil {
-		t.Fatal(err)
-	}
-	if err := os.MkdirAll("_recvonly/unknownDir", 0755); err != nil {
-		t.Fatal(err)
-	}
+	testOs.MkdirAll("_recvonly/.stfolder", 0755)
+	testOs.MkdirAll("_recvonly/ignDir", 0755)
+	testOs.MkdirAll("_recvonly/unknownDir", 0755)
 	if err := ioutil.WriteFile("_recvonly/ignDir/ignFile", []byte("hello\n"), 0644); err != nil {
 		t.Fatal(err)
 	}
@@ -125,23 +115,17 @@ func TestRecvOnlyRevertDeletes(t *testing.T) {
 }
 
 func TestRecvOnlyRevertNeeds(t *testing.T) {
+	testOs := &fatalOs{t}
+
 	// Make sure that a new file gets picked up and considered latest, then
 	// gets considered old when we hit Revert.
 
-	if err := os.RemoveAll("_recvonly"); err != nil && !os.IsNotExist(err) {
-		t.Fatal(err)
-	}
-	defer func() {
-		if err := os.RemoveAll("_recvonly"); err != nil && !os.IsNotExist(err) {
-			t.Fatal(err)
-		}
-	}()
+	testOs.RemoveAll("_recvonly")
+	defer testOs.RemoveAll("_recvonly")
 
 	// Create some test data
 
-	if err := os.MkdirAll("_recvonly/.stfolder", 0755); err != nil {
-		t.Fatal(err)
-	}
+	testOs.MkdirAll("_recvonly/.stfolder", 0755)
 	oldData := []byte("hello\n")
 	knownFiles := setupKnownFiles(t, oldData)
 
@@ -231,20 +215,14 @@ func TestRecvOnlyRevertNeeds(t *testing.T) {
 }
 
 func TestRecvOnlyUndoChanges(t *testing.T) {
-	if err := os.RemoveAll("_recvonly"); err != nil && !os.IsNotExist(err) {
-		t.Fatal(err)
-	}
-	defer func() {
-		if err := os.RemoveAll("_recvonly"); err != nil && !os.IsNotExist(err) {
-			t.Fatal(err)
-		}
-	}()
+	testOs := &fatalOs{t}
+
+	testOs.RemoveAll("_recvonly")
+	defer testOs.RemoveAll("_recvonly")
 
 	// Create some test data
 
-	if err := os.MkdirAll("_recvonly/.stfolder", 0755); err != nil {
-		t.Fatal(err)
-	}
+	testOs.MkdirAll("_recvonly/.stfolder", 0755)
 	oldData := []byte("hello\n")
 	knownFiles := setupKnownFiles(t, oldData)
 
@@ -307,9 +285,7 @@ func TestRecvOnlyUndoChanges(t *testing.T) {
 
 	// Remove the file again and undo the modification
 
-	if err := os.Remove(file); err != nil {
-		t.Fatal(err)
-	}
+	testOs.Remove(file)
 	if err := ioutil.WriteFile("_recvonly/knownDir/knownFile", oldData, 0644); err != nil {
 		t.Fatal(err)
 	}
@@ -324,22 +300,17 @@ func TestRecvOnlyUndoChanges(t *testing.T) {
 }
 
 func setupKnownFiles(t *testing.T, data []byte) []protocol.FileInfo {
-	if err := os.MkdirAll("_recvonly/knownDir", 0755); err != nil {
-		t.Fatal(err)
-	}
+	testOs := &fatalOs{t}
+
+	testOs.MkdirAll("_recvonly/knownDir", 0755)
 	if err := ioutil.WriteFile("_recvonly/knownDir/knownFile", data, 0644); err != nil {
 		t.Fatal(err)
 	}
 
 	t0 := time.Now().Add(-1 * time.Minute)
-	if err := os.Chtimes("_recvonly/knownDir/knownFile", t0, t0); err != nil {
-		t.Fatal(err)
-	}
+	testOs.Chtimes("_recvonly/knownDir/knownFile", t0, t0)
 
-	fi, err := os.Stat("_recvonly/knownDir/knownFile")
-	if err != nil {
-		t.Fatal(err)
-	}
+	fi, _ := testOs.Stat("_recvonly/knownDir/knownFile")
 	blocks, _ := scanner.Blocks(context.TODO(), bytes.NewReader(data), protocol.BlockSize(int64(len(data))), int64(len(data)), nil, true)
 	knownFiles := []protocol.FileInfo{
 		{
diff --git a/lib/model/folder_sendrecv_test.go b/lib/model/folder_sendrecv_test.go
index e0f222c49..58a31134e 100644
--- a/lib/model/folder_sendrecv_test.go
+++ b/lib/model/folder_sendrecv_test.go
@@ -196,6 +196,8 @@ func TestHandleFileWithTemp(t *testing.T) {
 }
 
 func TestCopierFinder(t *testing.T) {
+	testOs := &fatalOs{t}
+
 	// After diff between required and existing we should:
 	// Copy: 1, 2, 3, 4, 6, 7, 8
 	// Since there is no existing file, nor a temp file
@@ -204,11 +206,8 @@ func TestCopierFinder(t *testing.T) {
 	// Pull: 1, 5, 6, 8
 
 	tempFile := filepath.Join("testdata", fs.TempName("file2"))
-	err := os.Remove(tempFile)
-	if err != nil && !os.IsNotExist(err) {
-		t.Error(err)
-	}
-	defer os.Remove(tempFile)
+	testOs.Remove(tempFile)
+	defer testOs.Remove(tempFile)
 
 	existingBlocks := []int{0, 2, 3, 4, 0, 0, 7, 0}
 	existingFile := setUpFile(fs.TempName("file"), existingBlocks)
@@ -273,6 +272,8 @@ func TestCopierFinder(t *testing.T) {
 }
 
 func TestWeakHash(t *testing.T) {
+	testOs := &fatalOs{t}
+
 	tempFile := filepath.Join("testdata", fs.TempName("weakhash"))
 	var shift int64 = 10
 	var size int64 = 1 << 20
@@ -284,19 +285,16 @@ func TestWeakHash(t *testing.T) {
 
 	cleanup := func() {
 		for _, path := range []string{tempFile, "testdata/weakhash"} {
-			os.Remove(path)
+			testOs.Remove(path)
 		}
 	}
 
 	cleanup()
 	defer cleanup()
 
-	f, err := os.Create("testdata/weakhash")
-	if err != nil {
-		t.Error(err)
-	}
+	f, _ := testOs.Create("testdata/weakhash")
 	defer f.Close()
-	_, err = io.CopyN(f, rand.Reader, size)
+	_, err := io.CopyN(f, rand.Reader, size)
 	if err != nil {
 		t.Error(err)
 	}
@@ -373,9 +371,7 @@ func TestWeakHash(t *testing.T) {
 	}
 
 	finish.fd.Close()
-	if err := os.Remove(tempFile); err != nil && !os.IsNotExist(err) {
-		t.Error(err)
-	}
+	testOs.Remove(tempFile)
 
 	// Test 2 - using weak hash, expectPulls blocks pulled.
 	fo.WeakHashThresholdPct = -1
@@ -438,8 +434,10 @@ func TestCopierCleanup(t *testing.T) {
 }
 
 func TestDeregisterOnFailInCopy(t *testing.T) {
+	testOs := &fatalOs{t}
+
 	file := setUpFile("filex", []int{0, 2, 0, 0, 5, 0, 0, 8})
-	defer os.Remove("testdata/" + fs.TempName("filex"))
+	defer testOs.Remove("testdata/" + fs.TempName("filex"))
 
 	db := db.OpenMemory()
 
@@ -530,8 +528,10 @@ func TestDeregisterOnFailInCopy(t *testing.T) {
 }
 
 func TestDeregisterOnFailInPull(t *testing.T) {
+	testOs := &fatalOs{t}
+
 	file := setUpFile("filex", []int{0, 2, 0, 0, 5, 0, 0, 8})
-	defer os.Remove("testdata/" + fs.TempName("filex"))
+	defer testOs.Remove("testdata/" + fs.TempName("filex"))
 
 	db := db.OpenMemory()
 	m := NewModel(defaultCfgWrapper, protocol.LocalDeviceID, "syncthing", "dev", db, nil)
diff --git a/lib/model/model_test.go b/lib/model/model_test.go
index 6b909db6f..fbb521b7e 100644
--- a/lib/model/model_test.go
+++ b/lib/model/model_test.go
@@ -74,7 +74,7 @@ func init() {
 			},
 		},
 		Options: config.OptionsConfiguration{
-			DefaultFolderPath: "testdata",
+			DefaultFolderPath: ".",
 		},
 	}
 }
@@ -114,7 +114,7 @@ func init() {
 func TestMain(m *testing.M) {
 	tmpLocation = "/tmp"
 	if runtime.GOOS == "windows" {
-		tmpLocation = filepath.Join("testdata", "tmp")
+		tmpLocation = "test-tmp"
 		if err := os.MkdirAll(tmpLocation, 0777); err != nil {
 			panic(err)
 		}
@@ -515,6 +515,8 @@ func BenchmarkRequestOut(b *testing.B) {
 }
 
 func BenchmarkRequestInSingleFile(b *testing.B) {
+	testOs := &fatalOs{b}
+
 	db := db.OpenMemory()
 	m := NewModel(defaultCfgWrapper, protocol.LocalDeviceID, "syncthing", "dev", db, nil)
 	m.AddFolder(defaultFolderConfig)
@@ -524,9 +526,9 @@ func BenchmarkRequestInSingleFile(b *testing.B) {
 
 	buf := make([]byte, 128<<10)
 	rand.Read(buf)
-	os.RemoveAll("testdata/request")
-	defer os.RemoveAll("testdata/request")
-	os.MkdirAll("testdata/request/for/a/file/in/a/couple/of/dirs", 0755)
+	testOs.RemoveAll("testdata/request")
+	defer testOs.RemoveAll("testdata/request")
+	testOs.MkdirAll("testdata/request/for/a/file/in/a/couple/of/dirs", 0755)
 	ioutil.WriteFile("testdata/request/for/a/file/in/a/couple/of/dirs/128k", buf, 0644)
 
 	b.ResetTimer()
@@ -541,11 +543,13 @@ func BenchmarkRequestInSingleFile(b *testing.B) {
 }
 
 func TestDeviceRename(t *testing.T) {
+	testOs := &fatalOs{t}
+
 	hello := protocol.HelloResult{
 		ClientName:    "syncthing",
 		ClientVersion: "v0.9.4",
 	}
-	defer os.Remove("testdata/tmpconfig.xml")
+	defer testOs.Remove("testdata/tmpconfig.xml")
 
 	rawCfg := config.New(device1)
 	rawCfg.Devices = []config.DeviceConfiguration{
@@ -613,6 +617,8 @@ func TestDeviceRename(t *testing.T) {
 }
 
 func TestClusterConfig(t *testing.T) {
+	testOs := &fatalOs{t}
+
 	cfg := config.New(device1)
 	cfg.Devices = []config.DeviceConfiguration{
 		{
@@ -654,7 +660,7 @@ func TestClusterConfig(t *testing.T) {
 	db := db.OpenMemory()
 
 	wrapper := createTmpWrapper(cfg)
-	defer os.Remove(wrapper.ConfigPath())
+	defer testOs.Remove(wrapper.ConfigPath())
 	m := NewModel(wrapper, protocol.LocalDeviceID, "syncthing", "dev", db, nil)
 	m.AddFolder(cfg.Folders[0])
 	m.AddFolder(cfg.Folders[1])
@@ -709,6 +715,8 @@ func TestClusterConfig(t *testing.T) {
 }
 
 func TestIntroducer(t *testing.T) {
+	testOs := &fatalOs{t}
+
 	var introducedByAnyone protocol.DeviceID
 
 	// LocalDeviceID is a magic value meaning don't check introducer
@@ -748,7 +756,7 @@ func TestIntroducer(t *testing.T) {
 			},
 		},
 	})
-	defer os.Remove(wcfg.ConfigPath())
+	defer testOs.Remove(wcfg.ConfigPath())
 	m.ClusterConfig(device1, protocol.ClusterConfig{
 		Folders: []protocol.Folder{
 			{
@@ -801,7 +809,7 @@ func TestIntroducer(t *testing.T) {
 			},
 		},
 	})
-	defer os.Remove(wcfg.ConfigPath())
+	defer testOs.Remove(wcfg.ConfigPath())
 	m.ClusterConfig(device1, protocol.ClusterConfig{
 		Folders: []protocol.Folder{
 			{
@@ -860,7 +868,7 @@ func TestIntroducer(t *testing.T) {
 			},
 		},
 	})
-	defer os.Remove(wcfg.ConfigPath())
+	defer testOs.Remove(wcfg.ConfigPath())
 	m.ClusterConfig(device1, protocol.ClusterConfig{})
 
 	if _, ok := wcfg.Device(device2); ok {
@@ -908,7 +916,7 @@ func TestIntroducer(t *testing.T) {
 			},
 		},
 	})
-	defer os.Remove(wcfg.ConfigPath())
+	defer testOs.Remove(wcfg.ConfigPath())
 	m.ClusterConfig(device1, protocol.ClusterConfig{})
 
 	if _, ok := wcfg.Device(device2); !ok {
@@ -955,7 +963,7 @@ func TestIntroducer(t *testing.T) {
 			},
 		},
 	})
-	defer os.Remove(wcfg.ConfigPath())
+	defer testOs.Remove(wcfg.ConfigPath())
 	m.ClusterConfig(device1, protocol.ClusterConfig{
 		Folders: []protocol.Folder{
 			{
@@ -1015,7 +1023,7 @@ func TestIntroducer(t *testing.T) {
 			},
 		},
 	})
-	defer os.Remove(wcfg.ConfigPath())
+	defer testOs.Remove(wcfg.ConfigPath())
 	m.ClusterConfig(device1, protocol.ClusterConfig{})
 
 	if _, ok := wcfg.Device(device2); !ok {
@@ -1062,7 +1070,7 @@ func TestIntroducer(t *testing.T) {
 			},
 		},
 	})
-	defer os.Remove(wcfg.ConfigPath())
+	defer testOs.Remove(wcfg.ConfigPath())
 	m.ClusterConfig(device1, protocol.ClusterConfig{})
 
 	if _, ok := wcfg.Device(device2); !ok {
@@ -1079,6 +1087,8 @@ func TestIntroducer(t *testing.T) {
 }
 
 func TestIssue4897(t *testing.T) {
+	testOs := &fatalOs{t}
+
 	wcfg, m := newState(config.Configuration{
 		Devices: []config.DeviceConfiguration{
 			{
@@ -1097,7 +1107,7 @@ func TestIssue4897(t *testing.T) {
 			},
 		},
 	})
-	defer os.Remove(wcfg.ConfigPath())
+	defer testOs.Remove(wcfg.ConfigPath())
 
 	cm := m.generateClusterConfig(device1)
 	if l := len(cm.Folders); l != 1 {
@@ -1106,8 +1116,10 @@ func TestIssue4897(t *testing.T) {
 }
 
 func TestIssue5063(t *testing.T) {
+	testOs := &fatalOs{t}
+
 	wcfg, m := newState(defaultAutoAcceptCfg)
-	defer os.Remove(wcfg.ConfigPath())
+	defer testOs.Remove(wcfg.ConfigPath())
 
 	addAndVerify := func(wg *sync.WaitGroup) {
 		id := srand.String(8)
@@ -1119,7 +1131,7 @@ func TestIssue5063(t *testing.T) {
 				},
 			},
 		})
-		os.RemoveAll(filepath.Join("testdata", id))
+		testOs.RemoveAll(id)
 		wg.Done()
 		if fcfg, ok := wcfg.Folder(id); !ok || !fcfg.SharedWith(device1) {
 			t.Error("expected shared", id)
@@ -1136,15 +1148,17 @@ func TestIssue5063(t *testing.T) {
 }
 
 func TestAutoAcceptRejected(t *testing.T) {
+	testOs := &fatalOs{t}
+
 	// Nothing happens if AutoAcceptFolders not set
 	tcfg := defaultAutoAcceptCfg.Copy()
 	for i := range tcfg.Devices {
 		tcfg.Devices[i].AutoAcceptFolders = false
 	}
 	wcfg, m := newState(tcfg)
-	defer os.Remove(wcfg.ConfigPath())
+	defer testOs.Remove(wcfg.ConfigPath())
 	id := srand.String(8)
-	defer os.RemoveAll(filepath.Join("testdata", id))
+	defer testOs.RemoveAll(id)
 	m.ClusterConfig(device1, protocol.ClusterConfig{
 		Folders: []protocol.Folder{
 			{
@@ -1160,11 +1174,13 @@ func TestAutoAcceptRejected(t *testing.T) {
 }
 
 func TestAutoAcceptNewFolder(t *testing.T) {
+	testOs := &fatalOs{t}
+
 	// New folder
 	wcfg, m := newState(defaultAutoAcceptCfg)
-	defer os.Remove(wcfg.ConfigPath())
+	defer testOs.Remove(wcfg.ConfigPath())
 	id := srand.String(8)
-	defer os.RemoveAll(filepath.Join("testdata", id))
+	defer testOs.RemoveAll(id)
 	m.ClusterConfig(device1, protocol.ClusterConfig{
 		Folders: []protocol.Folder{
 			{
@@ -1179,10 +1195,12 @@ func TestAutoAcceptNewFolder(t *testing.T) {
 }
 
 func TestAutoAcceptNewFolderFromTwoDevices(t *testing.T) {
+	testOs := &fatalOs{t}
+
 	wcfg, m := newState(defaultAutoAcceptCfg)
-	defer os.Remove(wcfg.ConfigPath())
+	defer testOs.Remove(wcfg.ConfigPath())
 	id := srand.String(8)
-	defer os.RemoveAll(filepath.Join("testdata", id))
+	defer testOs.RemoveAll(id)
 	m.ClusterConfig(device1, protocol.ClusterConfig{
 		Folders: []protocol.Folder{
 			{
@@ -1212,12 +1230,14 @@ func TestAutoAcceptNewFolderFromTwoDevices(t *testing.T) {
 }
 
 func TestAutoAcceptNewFolderFromOnlyOneDevice(t *testing.T) {
+	testOs := &fatalOs{t}
+
 	modifiedCfg := defaultAutoAcceptCfg.Copy()
 	modifiedCfg.Devices[2].AutoAcceptFolders = false
 	wcfg, m := newState(modifiedCfg)
-	defer os.Remove(wcfg.ConfigPath())
+	defer testOs.Remove(wcfg.ConfigPath())
 	id := srand.String(8)
-	defer os.RemoveAll(filepath.Join("testdata", id))
+	defer testOs.RemoveAll(id)
 	m.ClusterConfig(device1, protocol.ClusterConfig{
 		Folders: []protocol.Folder{
 			{
@@ -1250,6 +1270,9 @@ func TestAutoAcceptNewFolderPremutationsNoPanic(t *testing.T) {
 	if testing.Short() {
 		t.Skip("short tests only")
 	}
+
+	testOs := &fatalOs{t}
+
 	id := srand.String(8)
 	label := srand.String(8)
 	premutations := []protocol.Folder{
@@ -1265,12 +1288,12 @@ func TestAutoAcceptNewFolderPremutationsNoPanic(t *testing.T) {
 				for _, dev2folder := range premutations {
 					cfg := defaultAutoAcceptCfg.Copy()
 					if localFolder.Label != "" {
-						fcfg := config.NewFolderConfiguration(protocol.LocalDeviceID, localFolder.ID, localFolder.Label, fs.FilesystemTypeBasic, filepath.Join("testdata", localFolder.ID))
+						fcfg := config.NewFolderConfiguration(protocol.LocalDeviceID, localFolder.ID, localFolder.Label, fs.FilesystemTypeBasic, localFolder.ID)
 						fcfg.Paused = localFolderPaused
 						cfg.Folders = append(cfg.Folders, fcfg)
 					}
 					wcfg, m := newState(cfg)
-					defer os.Remove(wcfg.ConfigPath())
+					defer testOs.Remove(wcfg.ConfigPath())
 					m.ClusterConfig(device1, protocol.ClusterConfig{
 						Folders: []protocol.Folder{dev1folder},
 					})
@@ -1278,8 +1301,8 @@ func TestAutoAcceptNewFolderPremutationsNoPanic(t *testing.T) {
 						Folders: []protocol.Folder{dev2folder},
 					})
 					m.Stop()
-					os.RemoveAll(filepath.Join("testdata", id))
-					os.RemoveAll(filepath.Join("testdata", label))
+					testOs.RemoveAll(id)
+					testOs.RemoveAll(label)
 				}
 			}
 		}
@@ -1287,13 +1310,15 @@ func TestAutoAcceptNewFolderPremutationsNoPanic(t *testing.T) {
 }
 
 func TestAutoAcceptMultipleFolders(t *testing.T) {
+	testOs := &fatalOs{t}
+
 	// Multiple new folders
 	wcfg, m := newState(defaultAutoAcceptCfg)
-	defer os.Remove(wcfg.ConfigPath())
+	defer testOs.Remove(wcfg.ConfigPath())
 	id1 := srand.String(8)
-	defer os.RemoveAll(filepath.Join("testdata", id1))
+	defer testOs.RemoveAll(id1)
 	id2 := srand.String(8)
-	defer os.RemoveAll(filepath.Join("testdata", id2))
+	defer testOs.RemoveAll(id2)
 	m.ClusterConfig(device1, protocol.ClusterConfig{
 		Folders: []protocol.Folder{
 			{
@@ -1315,21 +1340,23 @@ func TestAutoAcceptMultipleFolders(t *testing.T) {
 }
 
 func TestAutoAcceptExistingFolder(t *testing.T) {
+	testOs := &fatalOs{t}
+
 	// Existing folder
 	id := srand.String(8)
 	idOther := srand.String(8) // To check that path does not get changed.
-	defer os.RemoveAll(filepath.Join("testdata", id))
-	defer os.RemoveAll(filepath.Join("testdata", idOther))
+	defer testOs.RemoveAll(id)
+	defer testOs.RemoveAll(idOther)
 
 	tcfg := defaultAutoAcceptCfg.Copy()
 	tcfg.Folders = []config.FolderConfiguration{
 		{
 			ID:   id,
-			Path: filepath.Join("testdata", idOther), // To check that path does not get changed.
+			Path: idOther, // To check that path does not get changed.
 		},
 	}
 	wcfg, m := newState(tcfg)
-	defer os.Remove(wcfg.ConfigPath())
+	defer testOs.Remove(wcfg.ConfigPath())
 	if fcfg, ok := wcfg.Folder(id); !ok || fcfg.SharedWith(device1) {
 		t.Error("missing folder, or shared", id)
 	}
@@ -1342,27 +1369,29 @@ func TestAutoAcceptExistingFolder(t *testing.T) {
 		},
 	})
 
-	if fcfg, ok := wcfg.Folder(id); !ok || !fcfg.SharedWith(device1) || fcfg.Path != filepath.Join("testdata", idOther) {
+	if fcfg, ok := wcfg.Folder(id); !ok || !fcfg.SharedWith(device1) || fcfg.Path != idOther {
 		t.Error("missing folder, or unshared, or path changed", id)
 	}
 }
 
 func TestAutoAcceptNewAndExistingFolder(t *testing.T) {
+	testOs := &fatalOs{t}
+
 	// New and existing folder
 	id1 := srand.String(8)
-	defer os.RemoveAll(filepath.Join("testdata", id1))
+	defer testOs.RemoveAll(id1)
 	id2 := srand.String(8)
-	defer os.RemoveAll(filepath.Join("testdata", id2))
+	defer testOs.RemoveAll(id2)
 
 	tcfg := defaultAutoAcceptCfg.Copy()
 	tcfg.Folders = []config.FolderConfiguration{
 		{
 			ID:   id1,
-			Path: filepath.Join("testdata", id1), // from previous test case, to verify that path doesn't get changed.
+			Path: id1, // from previous test case, to verify that path doesn't get changed.
 		},
 	}
 	wcfg, m := newState(tcfg)
-	defer os.Remove(wcfg.ConfigPath())
+	defer testOs.Remove(wcfg.ConfigPath())
 	if fcfg, ok := wcfg.Folder(id1); !ok || fcfg.SharedWith(device1) {
 		t.Error("missing folder, or shared", id1)
 	}
@@ -1387,14 +1416,16 @@ func TestAutoAcceptNewAndExistingFolder(t *testing.T) {
 }
 
 func TestAutoAcceptAlreadyShared(t *testing.T) {
+	testOs := &fatalOs{t}
+
 	// Already shared
 	id := srand.String(8)
-	defer os.RemoveAll(filepath.Join("testdata", id))
+	defer testOs.RemoveAll(id)
 	tcfg := defaultAutoAcceptCfg.Copy()
 	tcfg.Folders = []config.FolderConfiguration{
 		{
 			ID:   id,
-			Path: filepath.Join("testdata", id),
+			Path: id,
 			Devices: []config.FolderDeviceConfiguration{
 				{
 					DeviceID: device1,
@@ -1403,7 +1434,7 @@ func TestAutoAcceptAlreadyShared(t *testing.T) {
 		},
 	}
 	wcfg, m := newState(tcfg)
-	defer os.Remove(wcfg.ConfigPath())
+	defer testOs.Remove(wcfg.ConfigPath())
 	if fcfg, ok := wcfg.Folder(id); !ok || !fcfg.SharedWith(device1) {
 		t.Error("missing folder, or not shared", id)
 	}
@@ -1422,14 +1453,16 @@ func TestAutoAcceptAlreadyShared(t *testing.T) {
 }
 
 func TestAutoAcceptNameConflict(t *testing.T) {
+	testOs := &fatalOs{t}
+
 	id := srand.String(8)
 	label := srand.String(8)
-	os.MkdirAll(filepath.Join("testdata", id), 0777)
-	os.MkdirAll(filepath.Join("testdata", label), 0777)
-	defer os.RemoveAll(filepath.Join("testdata", id))
-	defer os.RemoveAll(filepath.Join("testdata", label))
+	testOs.MkdirAll(id, 0777)
+	testOs.MkdirAll(label, 0777)
+	defer testOs.RemoveAll(id)
+	defer testOs.RemoveAll(label)
 	wcfg, m := newState(defaultAutoAcceptCfg)
-	defer os.Remove(wcfg.ConfigPath())
+	defer testOs.Remove(wcfg.ConfigPath())
 	m.ClusterConfig(device1, protocol.ClusterConfig{
 		Folders: []protocol.Folder{
 			{
@@ -1444,13 +1477,15 @@ func TestAutoAcceptNameConflict(t *testing.T) {
 }
 
 func TestAutoAcceptPrefersLabel(t *testing.T) {
+	testOs := &fatalOs{t}
+
 	// Prefers label, falls back to ID.
 	wcfg, m := newState(defaultAutoAcceptCfg)
-	defer os.Remove(wcfg.ConfigPath())
+	defer testOs.Remove(wcfg.ConfigPath())
 	id := srand.String(8)
 	label := srand.String(8)
-	defer os.RemoveAll(filepath.Join("testdata", id))
-	defer os.RemoveAll(filepath.Join("testdata", label))
+	defer testOs.RemoveAll(id)
+	defer testOs.RemoveAll(label)
 	m.ClusterConfig(device1, protocol.ClusterConfig{
 		Folders: []protocol.Folder{
 			{
@@ -1465,14 +1500,17 @@ func TestAutoAcceptPrefersLabel(t *testing.T) {
 }
 
 func TestAutoAcceptFallsBackToID(t *testing.T) {
+	testOs := &fatalOs{t}
+
 	// Prefers label, falls back to ID.
 	wcfg, m := newState(defaultAutoAcceptCfg)
-	defer os.Remove(wcfg.ConfigPath())
+	defer testOs.Remove(wcfg.ConfigPath())
 	id := srand.String(8)
 	label := srand.String(8)
-	os.MkdirAll(filepath.Join("testdata", label), 0777)
-	defer os.RemoveAll(filepath.Join("testdata", label))
-	defer os.RemoveAll(filepath.Join("testdata", id))
+	t.Log(id, label)
+	testOs.MkdirAll(label, 0777)
+	defer testOs.RemoveAll(label)
+	defer testOs.RemoveAll(id)
 	m.ClusterConfig(device1, protocol.ClusterConfig{
 		Folders: []protocol.Folder{
 			{
@@ -1487,14 +1525,16 @@ func TestAutoAcceptFallsBackToID(t *testing.T) {
 }
 
 func TestAutoAcceptPausedWhenFolderConfigChanged(t *testing.T) {
+	testOs := &fatalOs{t}
+
 	// Existing folder
 	id := srand.String(8)
 	idOther := srand.String(8) // To check that path does not get changed.
-	defer os.RemoveAll(filepath.Join("testdata", id))
-	defer os.RemoveAll(filepath.Join("testdata", idOther))
+	defer testOs.RemoveAll(id)
+	defer testOs.RemoveAll(idOther)
 
 	tcfg := defaultAutoAcceptCfg.Copy()
-	fcfg := config.NewFolderConfiguration(protocol.LocalDeviceID, id, "", fs.FilesystemTypeBasic, filepath.Join("testdata", idOther))
+	fcfg := config.NewFolderConfiguration(protocol.LocalDeviceID, id, "", fs.FilesystemTypeBasic, idOther)
 	fcfg.Paused = true
 	// The order of devices here is wrong (cfg.clean() sorts them), which will cause the folder to restart.
 	// Because of the restart, folder gets removed from m.deviceFolder, which means that generateClusterConfig will not panic.
@@ -1504,7 +1544,7 @@ func TestAutoAcceptPausedWhenFolderConfigChanged(t *testing.T) {
 	})
 	tcfg.Folders = []config.FolderConfiguration{fcfg}
 	wcfg, m := newState(tcfg)
-	defer os.Remove(wcfg.ConfigPath())
+	defer testOs.Remove(wcfg.ConfigPath())
 	if fcfg, ok := wcfg.Folder(id); !ok || !fcfg.SharedWith(device1) {
 		t.Error("missing folder, or not shared", id)
 	}
@@ -1524,7 +1564,7 @@ func TestAutoAcceptPausedWhenFolderConfigChanged(t *testing.T) {
 
 	if fcfg, ok := wcfg.Folder(id); !ok {
 		t.Error("missing folder")
-	} else if fcfg.Path != filepath.Join("testdata", idOther) {
+	} else if fcfg.Path != idOther {
 		t.Error("folder path changed")
 	} else {
 		for _, dev := range fcfg.DeviceIDs() {
@@ -1541,14 +1581,16 @@ func TestAutoAcceptPausedWhenFolderConfigChanged(t *testing.T) {
 }
 
 func TestAutoAcceptPausedWhenFolderConfigNotChanged(t *testing.T) {
+	testOs := &fatalOs{t}
+
 	// Existing folder
 	id := srand.String(8)
 	idOther := srand.String(8) // To check that path does not get changed.
-	defer os.RemoveAll(filepath.Join("testdata", id))
-	defer os.RemoveAll(filepath.Join("testdata", idOther))
+	defer testOs.RemoveAll(id)
+	defer testOs.RemoveAll(idOther)
 
 	tcfg := defaultAutoAcceptCfg.Copy()
-	fcfg := config.NewFolderConfiguration(protocol.LocalDeviceID, id, "", fs.FilesystemTypeBasic, filepath.Join("testdata", idOther))
+	fcfg := config.NewFolderConfiguration(protocol.LocalDeviceID, id, "", fs.FilesystemTypeBasic, idOther)
 	fcfg.Paused = true
 	// The new folder is exactly the same as the one constructed by handleAutoAccept, which means
 	// the folder will not be restarted (even if it's paused), yet handleAutoAccept used to add the folder
@@ -1561,7 +1603,7 @@ func TestAutoAcceptPausedWhenFolderConfigNotChanged(t *testing.T) {
 	}, fcfg.Devices...) // Need to ensure this device order to avoid folder restart.
 	tcfg.Folders = []config.FolderConfiguration{fcfg}
 	wcfg, m := newState(tcfg)
-	defer os.Remove(wcfg.ConfigPath())
+	defer testOs.Remove(wcfg.ConfigPath())
 	if fcfg, ok := wcfg.Folder(id); !ok || !fcfg.SharedWith(device1) {
 		t.Error("missing folder, or not shared", id)
 	}
@@ -1581,7 +1623,7 @@ func TestAutoAcceptPausedWhenFolderConfigNotChanged(t *testing.T) {
 
 	if fcfg, ok := wcfg.Folder(id); !ok {
 		t.Error("missing folder")
-	} else if fcfg.Path != filepath.Join("testdata", idOther) {
+	} else if fcfg.Path != idOther {
 		t.Error("folder path changed")
 	} else {
 		for _, dev := range fcfg.DeviceIDs() {
@@ -1658,9 +1700,11 @@ func changeIgnores(t *testing.T, m *Model, expected []string) {
 }
 
 func TestIgnores(t *testing.T) {
+	testOs := &fatalOs{t}
+
 	// Assure a clean start state
-	os.RemoveAll(filepath.Join("testdata", config.DefaultMarkerName))
-	os.MkdirAll(filepath.Join("testdata", config.DefaultMarkerName), 0644)
+	testOs.RemoveAll(filepath.Join("testdata", config.DefaultMarkerName))
+	testOs.MkdirAll(filepath.Join("testdata", config.DefaultMarkerName), 0644)
 	ioutil.WriteFile("testdata/.stignore", []byte(".*\nquux\n"), 0644)
 
 	db := db.OpenMemory()
@@ -1719,12 +1763,16 @@ func TestIgnores(t *testing.T) {
 	changeIgnores(t, m, expected)
 
 	// Make sure no .stignore file is considered valid
-	os.Rename("testdata/.stignore", "testdata/.stignore.bak")
+	defer func() {
+		testOs.Rename("testdata/.stignore.bak", "testdata/.stignore")
+	}()
+	testOs.Rename("testdata/.stignore", "testdata/.stignore.bak")
 	changeIgnores(t, m, []string{})
-	os.Rename("testdata/.stignore.bak", "testdata/.stignore")
 }
 
 func TestROScanRecovery(t *testing.T) {
+	testOs := &fatalOs{t}
+
 	ldb := db.OpenMemory()
 	set := db.NewFileSet("default", defaultFs, ldb)
 	set.Update(protocol.LocalDeviceID, []protocol.FileInfo{
@@ -1733,7 +1781,7 @@ func TestROScanRecovery(t *testing.T) {
 
 	fcfg := config.FolderConfiguration{
 		ID:              "default",
-		Path:            "testdata/rotestfolder",
+		Path:            "rotestfolder",
 		Type:            config.FolderTypeSendOnly,
 		RescanIntervalS: 1,
 		MarkerName:      config.DefaultMarkerName,
@@ -1746,9 +1794,9 @@ func TestROScanRecovery(t *testing.T) {
 			},
 		},
 	})
-	defer os.Remove(cfg.ConfigPath())
+	defer testOs.Remove(cfg.ConfigPath())
 
-	os.RemoveAll(fcfg.Path)
+	testOs.RemoveAll(fcfg.Path)
 
 	m := NewModel(cfg, protocol.LocalDeviceID, "syncthing", "dev", ldb, nil)
 	m.AddFolder(fcfg)
@@ -1779,18 +1827,14 @@ func TestROScanRecovery(t *testing.T) {
 		return
 	}
 
-	os.Mkdir(fcfg.Path, 0700)
+	testOs.Mkdir(fcfg.Path, 0700)
 
 	if err := waitFor("folder marker missing"); err != nil {
 		t.Error(err)
 		return
 	}
 
-	fd, err := os.Create(filepath.Join(fcfg.Path, config.DefaultMarkerName))
-	if err != nil {
-		t.Error(err)
-		return
-	}
+	fd, _ := testOs.Create(filepath.Join(fcfg.Path, config.DefaultMarkerName))
 	fd.Close()
 
 	if err := waitFor(""); err != nil {
@@ -1798,14 +1842,14 @@ func TestROScanRecovery(t *testing.T) {
 		return
 	}
 
-	os.Remove(filepath.Join(fcfg.Path, config.DefaultMarkerName))
+	testOs.Remove(filepath.Join(fcfg.Path, config.DefaultMarkerName))
 
 	if err := waitFor("folder marker missing"); err != nil {
 		t.Error(err)
 		return
 	}
 
-	os.Remove(fcfg.Path)
+	testOs.Remove(fcfg.Path)
 
 	if err := waitFor("folder path missing"); err != nil {
 		t.Error(err)
@@ -1814,6 +1858,8 @@ func TestROScanRecovery(t *testing.T) {
 }
 
 func TestRWScanRecovery(t *testing.T) {
+	testOs := &fatalOs{t}
+
 	ldb := db.OpenMemory()
 	set := db.NewFileSet("default", defaultFs, ldb)
 	set.Update(protocol.LocalDeviceID, []protocol.FileInfo{
@@ -1822,7 +1868,7 @@ func TestRWScanRecovery(t *testing.T) {
 
 	fcfg := config.FolderConfiguration{
 		ID:              "default",
-		Path:            "testdata/rwtestfolder",
+		Path:            "rwtestfolder",
 		Type:            config.FolderTypeSendReceive,
 		RescanIntervalS: 1,
 		MarkerName:      config.DefaultMarkerName,
@@ -1835,9 +1881,9 @@ func TestRWScanRecovery(t *testing.T) {
 			},
 		},
 	})
-	defer os.Remove(cfg.ConfigPath())
+	defer testOs.Remove(cfg.ConfigPath())
 
-	os.RemoveAll(fcfg.Path)
+	testOs.RemoveAll(fcfg.Path)
 
 	m := NewModel(cfg, protocol.LocalDeviceID, "syncthing", "dev", ldb, nil)
 	m.AddFolder(fcfg)
@@ -1868,37 +1914,33 @@ func TestRWScanRecovery(t *testing.T) {
 		return
 	}
 
-	os.Mkdir(fcfg.Path, 0700)
+	testOs.Mkdir(fcfg.Path, 0700)
 
 	if err := waitFor("folder marker missing"); err != nil {
 		t.Error(err)
 		return
 	}
 
-	fd, err := os.Create(filepath.Join(fcfg.Path, config.DefaultMarkerName))
+	fd, err := testOs.Create(filepath.Join(fcfg.Path, config.DefaultMarkerName))
 	if err != nil {
-		t.Error(err)
-		return
+		t.Fatal(err)
 	}
 	fd.Close()
 
 	if err := waitFor(""); err != nil {
-		t.Error(err)
-		return
+		t.Fatal(err)
 	}
 
-	os.Remove(filepath.Join(fcfg.Path, config.DefaultMarkerName))
+	testOs.Remove(filepath.Join(fcfg.Path, config.DefaultMarkerName))
 
 	if err := waitFor("folder marker missing"); err != nil {
-		t.Error(err)
-		return
+		t.Fatal(err)
 	}
 
-	os.Remove(fcfg.Path)
+	testOs.Remove(fcfg.Path)
 
 	if err := waitFor("folder path missing"); err != nil {
-		t.Error(err)
-		return
+		t.Fatal(err)
 	}
 }
 
@@ -2348,16 +2390,18 @@ func benchmarkTree(b *testing.B, n1, n2 int) {
 }
 
 func TestIssue3028(t *testing.T) {
+	testOs := &fatalOs{t}
+
 	// Create two files that we'll delete, one with a name that is a prefix of the other.
 
 	if err := ioutil.WriteFile("testdata/testrm", []byte("Hello"), 0644); err != nil {
 		t.Fatal(err)
 	}
-	defer os.Remove("testdata/testrm")
+	defer testOs.Remove("testdata/testrm")
 	if err := ioutil.WriteFile("testdata/testrm2", []byte("Hello"), 0644); err != nil {
 		t.Fatal(err)
 	}
-	defer os.Remove("testdata/testrm2")
+	defer testOs.Remove("testdata/testrm2")
 
 	// Create a model and default folder
 
@@ -2379,8 +2423,8 @@ func TestIssue3028(t *testing.T) {
 
 	// Delete and rescan specifically these two
 
-	os.Remove("testdata/testrm")
-	os.Remove("testdata/testrm2")
+	testOs.Remove("testdata/testrm")
+	testOs.Remove("testdata/testrm2")
 	m.ScanFolderSubdirs("default", []string{"testrm", "testrm2"})
 
 	// Verify that the number of files decreased by two and the number of
@@ -2403,11 +2447,13 @@ func TestIssue3028(t *testing.T) {
 }
 
 func TestIssue4357(t *testing.T) {
+	testOs := &fatalOs{t}
+
 	db := db.OpenMemory()
 	cfg := defaultCfgWrapper.RawCopy()
 	// Create a separate wrapper not to pollute other tests.
 	wrapper := createTmpWrapper(config.Configuration{})
-	defer os.Remove(wrapper.ConfigPath())
+	defer testOs.Remove(wrapper.ConfigPath())
 	m := NewModel(wrapper, protocol.LocalDeviceID, "syncthing", "dev", db, nil)
 	m.ServeBackground()
 	defer m.Stop()
@@ -2480,6 +2526,8 @@ func TestIssue4357(t *testing.T) {
 }
 
 func TestIssue2782(t *testing.T) {
+	testOs := &fatalOs{t}
+
 	// CheckHealth should accept a symlinked folder, when using tilde-expanded path.
 
 	if runtime.GOOS == "windows" {
@@ -2509,7 +2557,7 @@ func TestIssue2782(t *testing.T) {
 	if err := os.Symlink("syncdir", testDir+"/synclink"); err != nil {
 		t.Skip(err)
 	}
-	defer os.RemoveAll(testDir)
+	defer testOs.RemoveAll(testDir)
 
 	db := db.OpenMemory()
 	m := NewModel(defaultCfgWrapper, protocol.LocalDeviceID, "syncthing", "dev", db, nil)
@@ -2556,6 +2604,8 @@ func TestIndexesForUnknownDevicesDropped(t *testing.T) {
 }
 
 func TestSharedWithClearedOnDisconnect(t *testing.T) {
+	testOs := &fatalOs{t}
+
 	dbi := db.OpenMemory()
 
 	fcfg := config.NewFolderConfiguration(protocol.LocalDeviceID, "default", "default", fs.FilesystemTypeBasic, "testdata")
@@ -2576,7 +2626,7 @@ func TestSharedWithClearedOnDisconnect(t *testing.T) {
 	}
 
 	wcfg := createTmpWrapper(cfg)
-	defer os.Remove(wcfg.ConfigPath())
+	defer testOs.Remove(wcfg.ConfigPath())
 
 	m := NewModel(wcfg, protocol.LocalDeviceID, "syncthing", "dev", dbi, nil)
 	m.AddFolder(fcfg)
@@ -2794,6 +2844,8 @@ func TestIssue3829(t *testing.T) {
 func TestNoRequestsFromPausedDevices(t *testing.T) {
 	t.Skip("broken, fails randomly, #3843")
 
+	testOs := &fatalOs{t}
+
 	dbi := db.OpenMemory()
 
 	fcfg := config.NewFolderConfiguration(protocol.LocalDeviceID, "default", "default", fs.FilesystemTypeBasic, "testdata")
@@ -2814,7 +2866,7 @@ func TestNoRequestsFromPausedDevices(t *testing.T) {
 	}
 
 	wcfg := createTmpWrapper(cfg)
-	defer os.Remove(wcfg.ConfigPath())
+	defer testOs.Remove(wcfg.ConfigPath())
 
 	m := NewModel(wcfg, protocol.LocalDeviceID, "syncthing", "dev", dbi, nil)
 	m.AddFolder(fcfg)
@@ -3066,6 +3118,8 @@ func TestInternalScan(t *testing.T) {
 }
 
 func TestCustomMarkerName(t *testing.T) {
+	testOs := &fatalOs{t}
+
 	ldb := db.OpenMemory()
 	set := db.NewFileSet("default", defaultFs, ldb)
 	set.Update(protocol.LocalDeviceID, []protocol.FileInfo{
@@ -3074,7 +3128,7 @@ func TestCustomMarkerName(t *testing.T) {
 
 	fcfg := config.FolderConfiguration{
 		ID:              "default",
-		Path:            "testdata/rwtestfolder",
+		Path:            "rwtestfolder",
 		Type:            config.FolderTypeSendReceive,
 		RescanIntervalS: 1,
 		MarkerName:      "myfile",
@@ -3087,10 +3141,10 @@ func TestCustomMarkerName(t *testing.T) {
 			},
 		},
 	})
-	defer os.Remove(cfg.ConfigPath())
+	defer testOs.Remove(cfg.ConfigPath())
 
-	os.RemoveAll(fcfg.Path)
-	defer os.RemoveAll(fcfg.Path)
+	testOs.RemoveAll(fcfg.Path)
+	defer testOs.RemoveAll(fcfg.Path)
 
 	m := NewModel(cfg, protocol.LocalDeviceID, "syncthing", "dev", ldb, nil)
 	m.AddFolder(fcfg)
@@ -3117,21 +3171,15 @@ func TestCustomMarkerName(t *testing.T) {
 	}
 
 	if err := waitFor("folder path missing"); err != nil {
-		t.Error(err)
-		return
+		t.Fatal(err)
 	}
 
-	os.Mkdir(fcfg.Path, 0700)
-	fd, err := os.Create(filepath.Join(fcfg.Path, "myfile"))
-	if err != nil {
-		t.Error(err)
-		return
-	}
+	testOs.Mkdir(fcfg.Path, 0700)
+	fd, _ := testOs.Create(filepath.Join(fcfg.Path, "myfile"))
 	fd.Close()
 
 	if err := waitFor(""); err != nil {
-		t.Error(err)
-		return
+		t.Fatal(err)
 	}
 }
 
@@ -3277,6 +3325,8 @@ func TestIssue4475(t *testing.T) {
 }
 
 func TestVersionRestore(t *testing.T) {
+	testOs := &fatalOs{t}
+
 	// We create a bunch of files which we restore
 	// In each file, we write the filename as the content
 	// We verify that the content matches at the expected filenames
@@ -3285,7 +3335,7 @@ func TestVersionRestore(t *testing.T) {
 	if err != nil {
 		t.Fatal(err)
 	}
-	defer os.RemoveAll(dir)
+	defer testOs.RemoveAll(dir)
 
 	dbi := db.OpenMemory()
 
@@ -3298,7 +3348,7 @@ func TestVersionRestore(t *testing.T) {
 		Folders: []config.FolderConfiguration{fcfg},
 	}
 	cfg := createTmpWrapper(rawConfig)
-	defer os.Remove(cfg.ConfigPath())
+	defer testOs.Remove(cfg.ConfigPath())
 
 	m := NewModel(cfg, protocol.LocalDeviceID, "syncthing", "dev", dbi, nil)
 	m.AddFolder(fcfg)
@@ -3489,10 +3539,12 @@ func TestVersionRestore(t *testing.T) {
 }
 
 func TestPausedFolders(t *testing.T) {
+	testOs := &fatalOs{t}
+
 	// Create a separate wrapper not to pollute other tests.
 	cfg := defaultCfgWrapper.RawCopy()
 	wrapper := createTmpWrapper(cfg)
-	defer os.Remove(wrapper.ConfigPath())
+	defer testOs.Remove(wrapper.ConfigPath())
 
 	db := db.OpenMemory()
 	m := NewModel(wrapper, protocol.LocalDeviceID, "syncthing", "dev", db, nil)
@@ -3523,17 +3575,19 @@ func TestPausedFolders(t *testing.T) {
 }
 
 func TestIssue4094(t *testing.T) {
+	testOs := &fatalOs{t}
+
 	db := db.OpenMemory()
 	// Create a separate wrapper not to pollute other tests.
 	wrapper := createTmpWrapper(config.Configuration{})
-	defer os.Remove(wrapper.ConfigPath())
+	defer testOs.Remove(wrapper.ConfigPath())
 	m := NewModel(wrapper, protocol.LocalDeviceID, "syncthing", "dev", db, nil)
 	m.ServeBackground()
 	defer m.Stop()
 
 	// Force the model to wire itself and add the folders
-	folderPath := "testdata/nonexistent"
-	defer os.RemoveAll(folderPath)
+	folderPath := "nonexistent"
+	defer testOs.RemoveAll(folderPath)
 	cfg := defaultCfgWrapper.RawCopy()
 	fcfg := config.FolderConfiguration{
 		ID:     "folder1",
@@ -3560,17 +3614,19 @@ func TestIssue4094(t *testing.T) {
 }
 
 func TestIssue4903(t *testing.T) {
+	testOs := &fatalOs{t}
+
 	db := db.OpenMemory()
 	// Create a separate wrapper not to pollute other tests.
 	wrapper := createTmpWrapper(config.Configuration{})
-	defer os.Remove(wrapper.ConfigPath())
+	defer testOs.Remove(wrapper.ConfigPath())
 	m := NewModel(wrapper, protocol.LocalDeviceID, "syncthing", "dev", db, nil)
 	m.ServeBackground()
 	defer m.Stop()
 
 	// Force the model to wire itself and add the folders
-	folderPath := "testdata/nonexistent"
-	defer os.RemoveAll(folderPath)
+	folderPath := "nonexistent"
+	defer testOs.RemoveAll(folderPath)
 	cfg := defaultCfgWrapper.RawCopy()
 	fcfg := config.FolderConfiguration{
 		ID:     "folder1",
@@ -3623,11 +3679,13 @@ func TestIssue5002(t *testing.T) {
 }
 
 func TestParentOfUnignored(t *testing.T) {
+	testOs := &fatalOs{t}
+
 	wcfg, m := newState(defaultCfg)
 	defer func() {
 		m.Stop()
 		defaultFolderConfig.Filesystem().Remove(".stignore")
-		os.Remove(wcfg.ConfigPath())
+		testOs.Remove(wcfg.ConfigPath())
 	}()
 
 	m.SetIgnores("default", []string{"!quux", "*"})
@@ -3658,12 +3716,13 @@ func addFakeConn(m *Model, dev protocol.DeviceID) *fakeConnection {
 	return fc
 }
 
+// TestFolderRestartZombies reproduces issue 5233, where multiple concurrent folder
+// restarts would leave more than one folder runner alive.
 func TestFolderRestartZombies(t *testing.T) {
-	// This is for issue 5233, where multiple concurrent folder restarts
-	// would leave more than one folder runner alive.
+	testOs := &fatalOs{t}
 
 	wrapper := createTmpWrapper(defaultCfg.Copy())
-	defer os.Remove(wrapper.ConfigPath())
+	defer testOs.Remove(wrapper.ConfigPath())
 	folderCfg, _ := wrapper.Folder("default")
 	folderCfg.FilesystemType = fs.FilesystemTypeFake
 	wrapper.SetFolder(folderCfg)
@@ -3758,6 +3817,8 @@ func (c *alwaysChanged) Changed() bool {
 }
 
 func TestRequestLimit(t *testing.T) {
+	testOs := &fatalOs{t}
+
 	cfg := defaultCfg.Copy()
 	cfg.Devices = append(cfg.Devices, config.NewDeviceConfiguration(device2, "device2"))
 	cfg.Devices[1].MaxRequestKiB = 1
@@ -3767,7 +3828,7 @@ func TestRequestLimit(t *testing.T) {
 	}
 	m, _, wrapper := setupModelWithConnectionManual(cfg)
 	defer m.Stop()
-	defer os.Remove(wrapper.ConfigPath())
+	defer testOs.Remove(wrapper.ConfigPath())
 
 	file := "tmpfile"
 	befReq := time.Now()
diff --git a/lib/model/progressemitter_test.go b/lib/model/progressemitter_test.go
index 2f5ec6ac0..73947bee2 100644
--- a/lib/model/progressemitter_test.go
+++ b/lib/model/progressemitter_test.go
@@ -8,7 +8,6 @@ package model
 
 import (
 	"fmt"
-	"os"
 	"path/filepath"
 	"runtime"
 	"testing"
@@ -52,10 +51,12 @@ func expectTimeout(w *events.Subscription, t *testing.T) {
 }
 
 func TestProgressEmitter(t *testing.T) {
+	testOs := &fatalOs{t}
+
 	w := events.Default.Subscribe(events.DownloadProgress)
 
 	c := createTmpWrapper(config.Configuration{})
-	defer os.Remove(c.ConfigPath())
+	defer testOs.Remove(c.ConfigPath())
 	c.SetOptions(config.OptionsConfiguration{
 		ProgressUpdateIntervalS: 0,
 	})
@@ -103,8 +104,10 @@ func TestProgressEmitter(t *testing.T) {
 }
 
 func TestSendDownloadProgressMessages(t *testing.T) {
+	testOs := &fatalOs{t}
+
 	c := createTmpWrapper(config.Configuration{})
-	defer os.Remove(c.ConfigPath())
+	defer testOs.Remove(c.ConfigPath())
 	c.SetOptions(config.OptionsConfiguration{
 		ProgressUpdateIntervalS: 0,
 		TempIndexMinBlocks:      10,
diff --git a/lib/model/requests_test.go b/lib/model/requests_test.go
index 1a48ec37f..c6d9e3d1f 100644
--- a/lib/model/requests_test.go
+++ b/lib/model/requests_test.go
@@ -26,14 +26,16 @@ import (
 )
 
 func TestRequestSimple(t *testing.T) {
+	testOs := &fatalOs{t}
+
 	// Verify that the model performs a request and creates a file based on
 	// an incoming index update.
 
 	m, fc, tmpDir, w := setupModelWithConnection()
 	defer func() {
 		m.Stop()
-		os.RemoveAll(tmpDir)
-		os.Remove(w.ConfigPath())
+		testOs.RemoveAll(tmpDir)
+		testOs.Remove(w.ConfigPath())
 	}()
 
 	// We listen for incoming index updates and trigger when we see one for
@@ -63,6 +65,8 @@ func TestRequestSimple(t *testing.T) {
 }
 
 func TestSymlinkTraversalRead(t *testing.T) {
+	testOs := &fatalOs{t}
+
 	// Verify that a symlink can not be traversed for reading.
 
 	if runtime.GOOS == "windows" {
@@ -73,8 +77,8 @@ func TestSymlinkTraversalRead(t *testing.T) {
 	m, fc, tmpDir, w := setupModelWithConnection()
 	defer func() {
 		m.Stop()
-		os.RemoveAll(tmpDir)
-		os.Remove(w.ConfigPath())
+		testOs.RemoveAll(tmpDir)
+		testOs.Remove(w.ConfigPath())
 	}()
 
 	// We listen for incoming index updates and trigger when we see one for
@@ -105,6 +109,8 @@ func TestSymlinkTraversalRead(t *testing.T) {
 }
 
 func TestSymlinkTraversalWrite(t *testing.T) {
+	testOs := &fatalOs{t}
+
 	// Verify that a symlink can not be traversed for writing.
 
 	if runtime.GOOS == "windows" {
@@ -115,8 +121,8 @@ func TestSymlinkTraversalWrite(t *testing.T) {
 	m, fc, tmpDir, w := setupModelWithConnection()
 	defer func() {
 		m.Stop()
-		os.RemoveAll(tmpDir)
-		os.Remove(w.ConfigPath())
+		testOs.RemoveAll(tmpDir)
+		testOs.Remove(w.ConfigPath())
 	}()
 
 	// We listen for incoming index updates and trigger when we see one for
@@ -173,13 +179,15 @@ func TestSymlinkTraversalWrite(t *testing.T) {
 }
 
 func TestRequestCreateTmpSymlink(t *testing.T) {
+	testOs := &fatalOs{t}
+
 	// Test that an update for a temporary file is invalidated
 
 	m, fc, tmpDir, w := setupModelWithConnection()
 	defer func() {
 		m.Stop()
-		os.RemoveAll(tmpDir)
-		os.Remove(w.ConfigPath())
+		testOs.RemoveAll(tmpDir)
+		testOs.Remove(w.ConfigPath())
 	}()
 
 	// We listen for incoming index updates and trigger when we see one for
@@ -213,6 +221,8 @@ func TestRequestCreateTmpSymlink(t *testing.T) {
 }
 
 func TestRequestVersioningSymlinkAttack(t *testing.T) {
+	testOs := &fatalOs{t}
+
 	if runtime.GOOS == "windows" {
 		t.Skip("no symlink support on Windows")
 	}
@@ -221,7 +231,7 @@ func TestRequestVersioningSymlinkAttack(t *testing.T) {
 	// deleted symlink to escape
 
 	tmpDir := createTmpDir()
-	defer os.RemoveAll(tmpDir)
+	defer testOs.RemoveAll(tmpDir)
 
 	cfg := defaultCfgWrapper.RawCopy()
 	cfg.Devices = append(cfg.Devices, config.NewDeviceConfiguration(device2, "device2"))
@@ -234,7 +244,7 @@ func TestRequestVersioningSymlinkAttack(t *testing.T) {
 		Type: "trashcan",
 	}
 	w := createTmpWrapper(cfg)
-	defer os.Remove(w.ConfigPath())
+	defer testOs.Remove(w.ConfigPath())
 
 	db := db.OpenMemory()
 	m := NewModel(w, device1, "syncthing", "dev", db, nil)
@@ -243,7 +253,7 @@ func TestRequestVersioningSymlinkAttack(t *testing.T) {
 	m.StartFolder("default")
 	defer m.Stop()
 
-	defer os.RemoveAll(tmpDir)
+	defer testOs.RemoveAll(tmpDir)
 
 	fc := addFakeConn(m, device2)
 	fc.folder = "default"
@@ -309,6 +319,8 @@ func TestPullInvalidIgnoredSR(t *testing.T) {
 func pullInvalidIgnored(t *testing.T, ft config.FolderType) {
 	t.Helper()
 
+	testOs := &fatalOs{t}
+
 	tmpDir := createTmpDir()
 	cfg := defaultCfgWrapper.RawCopy()
 	cfg.Devices = append(cfg.Devices, config.NewDeviceConfiguration(device2, "device2"))
@@ -321,8 +333,8 @@ func pullInvalidIgnored(t *testing.T, ft config.FolderType) {
 	m, fc, w := setupModelWithConnectionManual(cfg)
 	defer func() {
 		m.Stop()
-		os.RemoveAll(tmpDir)
-		os.Remove(w.ConfigPath())
+		testOs.RemoveAll(tmpDir)
+		testOs.Remove(w.ConfigPath())
 	}()
 
 	// Reach in and update the ignore matcher to one that always does
@@ -440,11 +452,13 @@ func pullInvalidIgnored(t *testing.T, ft config.FolderType) {
 }
 
 func TestIssue4841(t *testing.T) {
+	testOs := &fatalOs{t}
+
 	m, fc, tmpDir, w := setupModelWithConnection()
 	defer func() {
 		m.Stop()
-		os.RemoveAll(tmpDir)
-		os.Remove(w.ConfigPath())
+		testOs.RemoveAll(tmpDir)
+		testOs.Remove(w.ConfigPath())
 	}()
 
 	received := make(chan protocol.FileInfo)
@@ -482,11 +496,13 @@ func TestIssue4841(t *testing.T) {
 }
 
 func TestRescanIfHaveInvalidContent(t *testing.T) {
+	testOs := &fatalOs{t}
+
 	m, fc, tmpDir, w := setupModelWithConnection()
 	defer func() {
 		m.Stop()
-		os.RemoveAll(tmpDir)
-		os.Remove(w.ConfigPath())
+		testOs.RemoveAll(tmpDir)
+		testOs.Remove(w.ConfigPath())
 	}()
 
 	payload := []byte("hello")
@@ -551,11 +567,13 @@ func TestRescanIfHaveInvalidContent(t *testing.T) {
 }
 
 func TestParentDeletion(t *testing.T) {
+	testOs := &fatalOs{t}
+
 	m, fc, tmpDir, w := setupModelWithConnection()
 	defer func() {
 		m.Stop()
-		os.RemoveAll(tmpDir)
-		os.Remove(w.ConfigPath())
+		testOs.RemoveAll(tmpDir)
+		testOs.Remove(w.ConfigPath())
 	}()
 
 	parent := "foo"
@@ -637,11 +655,13 @@ func TestRequestSymlinkWindows(t *testing.T) {
 		t.Skip("windows specific test")
 	}
 
+	testOs := &fatalOs{t}
+
 	m, fc, tmpDir, w := setupModelWithConnection()
 	defer func() {
 		m.Stop()
-		os.RemoveAll(tmpDir)
-		os.Remove(w.ConfigPath())
+		testOs.RemoveAll(tmpDir)
+		testOs.Remove(w.ConfigPath())
 	}()
 
 	first := make(chan struct{})
@@ -724,7 +744,7 @@ func setupModelWithConnectionManual(cfg config.Configuration) (*Model, *fakeConn
 }
 
 func createTmpDir() string {
-	tmpDir, err := ioutil.TempDir("testdata", "_request-")
+	tmpDir, err := ioutil.TempDir("", "_request-")
 	if err != nil {
 		panic("Failed to create temporary testing dir")
 	}
@@ -741,11 +761,13 @@ func equalContents(path string, contents []byte) error {
 }
 
 func TestRequestRemoteRenameChanged(t *testing.T) {
+	testOs := &fatalOs{t}
+
 	m, fc, tmpDir, w := setupModelWithConnection()
 	defer func() {
 		m.Stop()
-		os.RemoveAll(tmpDir)
-		os.Remove(w.ConfigPath())
+		testOs.RemoveAll(tmpDir)
+		testOs.Remove(w.ConfigPath())
 	}()
 	tfs := fs.NewFilesystem(fs.FilesystemTypeBasic, tmpDir)
 
@@ -823,11 +845,13 @@ func TestRequestRemoteRenameChanged(t *testing.T) {
 }
 
 func TestRequestRemoteRenameConflict(t *testing.T) {
+	testOs := &fatalOs{t}
+
 	m, fc, tmpDir, w := setupModelWithConnection()
 	defer func() {
 		m.Stop()
-		os.RemoveAll(tmpDir)
-		os.Remove(w.ConfigPath())
+		testOs.RemoveAll(tmpDir)
+		testOs.Remove(w.ConfigPath())
 	}()
 	tfs := fs.NewFilesystem(fs.FilesystemTypeBasic, tmpDir)
 
@@ -919,11 +943,13 @@ func TestRequestRemoteRenameConflict(t *testing.T) {
 }
 
 func TestRequestDeleteChanged(t *testing.T) {
+	testOs := &fatalOs{t}
+
 	m, fc, tmpDir, w := setupModelWithConnection()
 	defer func() {
 		m.Stop()
-		os.RemoveAll(tmpDir)
-		os.Remove(w.ConfigPath())
+		testOs.RemoveAll(tmpDir)
+		testOs.Remove(w.ConfigPath())
 	}()
 	tfs := fs.NewFilesystem(fs.FilesystemTypeBasic, tmpDir)
 
@@ -967,7 +993,7 @@ func TestRequestDeleteChanged(t *testing.T) {
 
 	// Check outcome
 	if _, err := tfs.Lstat(a); err != nil {
-		if os.IsNotExist(err) {
+		if fs.IsNotExist(err) {
 			t.Error(`Modified file "a" was removed`)
 		} else {
 			t.Error(`Error stating file "a":`, err)
diff --git a/lib/model/sharedpullerstate_test.go b/lib/model/sharedpullerstate_test.go
index ac01a659c..e4a6e38a4 100644
--- a/lib/model/sharedpullerstate_test.go
+++ b/lib/model/sharedpullerstate_test.go
@@ -7,7 +7,6 @@
 package model
 
 import (
-	"os"
 	"testing"
 
 	"github.com/syncthing/syncthing/lib/fs"
@@ -16,11 +15,13 @@ import (
 
 // Test creating temporary file inside read-only directory
 func TestReadOnlyDir(t *testing.T) {
+	testOs := &fatalOs{t}
+
 	// Create a read only directory, clean it up afterwards.
-	os.Mkdir("testdata/read_only_dir", 0555)
+	testOs.Mkdir("testdata/read_only_dir", 0555)
 	defer func() {
-		os.Chmod("testdata/read_only_dir", 0755)
-		os.RemoveAll("testdata/read_only_dir")
+		testOs.Chmod("testdata/read_only_dir", 0755)
+		testOs.RemoveAll("testdata/read_only_dir")
 	}()
 
 	s := sharedPullerState{
diff --git a/lib/model/testos_test.go b/lib/model/testos_test.go
new file mode 100644
index 000000000..3f01b68ee
--- /dev/null
+++ b/lib/model/testos_test.go
@@ -0,0 +1,82 @@
+// Copyright (C) 2019 The Syncthing Authors.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this file,
+// You can obtain one at https://mozilla.org/MPL/2.0/.
+
+package model
+
+import (
+	"os"
+	"time"
+)
+
+// fatal is the required common interface between *testing.B and *testing.T
+type fatal interface {
+	Fatal(...interface{})
+}
+
+type fatalOs struct {
+	fatal
+}
+
+func (f *fatalOs) must(fn func() error) {
+	if err := fn(); err != nil {
+		f.Fatal(err)
+	}
+}
+
+func (f *fatalOs) Chmod(name string, mode os.FileMode) error {
+	f.must(func() error { return os.Chmod(name, mode) })
+	return nil
+}
+
+func (f *fatalOs) Chtimes(name string, atime time.Time, mtime time.Time) error {
+	f.must(func() error { return os.Chtimes(name, atime, mtime) })
+	return nil
+}
+
+func (f *fatalOs) Create(name string) (*os.File, error) {
+	file, err := os.Create(name)
+	if err != nil {
+		f.Fatal(err)
+	}
+	return file, nil
+}
+
+func (f *fatalOs) Mkdir(name string, perm os.FileMode) error {
+	f.must(func() error { return os.Mkdir(name, perm) })
+	return nil
+}
+
+func (f *fatalOs) MkdirAll(name string, perm os.FileMode) error {
+	f.must(func() error { return os.MkdirAll(name, perm) })
+	return nil
+}
+
+func (f *fatalOs) Remove(name string) error {
+	if err := os.Remove(name); err != nil && !os.IsNotExist(err) {
+		f.Fatal(err)
+	}
+	return nil
+}
+
+func (f *fatalOs) RemoveAll(name string) error {
+	if err := os.RemoveAll(name); err != nil && !os.IsNotExist(err) {
+		f.Fatal(err)
+	}
+	return nil
+}
+
+func (f *fatalOs) Rename(oldname, newname string) error {
+	f.must(func() error { return os.Rename(oldname, newname) })
+	return nil
+}
+
+func (f *fatalOs) Stat(name string) (os.FileInfo, error) {
+	info, err := os.Stat(name)
+	if err != nil {
+		f.Fatal(err)
+	}
+	return info, nil
+}