diff: fix test failure and add remark on quiet to changelog

changelog/unreleased/issue-2508

@@ -1,8 +1,11 @@
-Enhancement: Support JSON output for diff
+Enhancement: Support JSON output and quiet mode for diff
 
 We've added support for getting machine-readable output for snapshot diff, just pass the
 flag `--json` for `restic diff` and restic will output a JSON-encoded diff stats and change
 list.
 
+Passing the `--quiet` flag to the `diff` command will only print the summary
+and suppress the detailed output.
+
 https://github.com/restic/restic/issues/2508
-https://github.com/restic/restic/pull/3592
+https://github.com/restic/restic/pull/3592

cmd/restic/integration_test.go

@@ -2011,19 +2011,26 @@ func TestDiff(t *testing.T) {
 	testRunBackup(t, "", []string{datadir}, opts, env.gopts)
 	_, secondSnapshotID := lastSnapshot(snapshots, loadSnapshotMap(t, env.gopts))
 
+	// quiet suppresses the diff output except for the summary
+	env.gopts.Quiet = false
 	_, err := testRunDiffOutput(env.gopts, "", secondSnapshotID)
 	rtest.Assert(t, err != nil, "expected error on invalid snapshot id")
 
 	out, err := testRunDiffOutput(env.gopts, firstSnapshotID, secondSnapshotID)
-	if err != nil {
-		t.Fatalf("expected no error from diff for test repository, got %v", err)
-	}
+	rtest.OK(t, err)
 
 	for _, pattern := range diffOutputRegexPatterns {
 		r, err := regexp.Compile(pattern)
 		rtest.Assert(t, err == nil, "failed to compile regexp %v", pattern)
 		rtest.Assert(t, r.MatchString(out), "expected pattern %v in output, got\n%v", pattern, out)
 	}
+
+	// check quiet output
+	env.gopts.Quiet = true
+	outQuiet, err := testRunDiffOutput(env.gopts, firstSnapshotID, secondSnapshotID)
+	rtest.OK(t, err)
+
+	rtest.Assert(t, len(outQuiet) < len(out), "expected shorter output on quiet mode %v vs. %v", len(outQuiet), len(out))
 }
 
 type writeToOnly struct {