Add initial test structure with test 'hosts' file.

.gitignore

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+test/tmp/*
+!test/tmp/.keep

test/fixtures/hosts

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+##
+# Host Database
+#
+# localhost is used to configure the loopback interface
+# when the system is booting.  Do not change this entry.
+##
+127.0.0.1	localhost
+255.255.255.255	broadcasthost
+::1             localhost
+fe80::1%lo0	localhost

test/hosts.bats

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+#!/usr/bin/env bats
+
+load test_helper
+
+@test "when passed no arguments exit with status 0" {
+  run "$_HOSTS"
+  [ "$status" -eq 0 ]
+}
+
+@test "when passed no arguments print enabled rules." {
+  run "$_HOSTS"
+  [[ "${lines[0]}" == "127.0.0.1	localhost" ]]
+  [[ "${lines[1]}" == "255.255.255.255	broadcasthost" ]]
+  [[ "${lines[2]}" == "::1             localhost" ]]
+  [[ "${lines[3]}" == "fe80::1%lo0	localhost" ]]
+  [[ "${lines[4]}" == "" ]]
+}

test/test_helper.bash

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+setup() {
+  # `$_HOSTS`
+  #
+  # The location of the `hosts` script being tested.
+  export _HOSTS="${BATS_TEST_DIRNAME}/../hosts"
+
+  export HOSTS_PATH="${BATS_TEST_DIRNAME}/tmp/hosts"
+  cp "${BATS_TEST_DIRNAME}/fixtures/hosts" "${BATS_TEST_DIRNAME}/tmp/hosts"
+}
+
+teardown() {
+  rm "${BATS_TEST_DIRNAME}/tmp/hosts"
+}