Go: What are testing.T.Cleanup and t.TempDir()?

1func TestWithCleanup(t *testing.T) {
2    // t.Cleanup runs AFTER test completion
3    t.Cleanup(func() {
4        os.RemoveAll("/tmp/test-data")
5        fmt.Println("Cleanup completed")
6    })
7
8    // Test...
9    os.MkdirAll("/tmp/test-data", 0755)
10    // ...
11}
12
13// TempDir: automatic creation and deletion of temporary directory
14func TestWithTempDir(t *testing.T) {
15    dir := t.TempDir()  // Creates a temporary directory
16    // Automatically removed after test!
17
18    err := os.WriteFile(filepath.Join(dir, "test.txt"), []byte("hello"), 0644)
19    if err != nil {
20        t.Fatal(err)
21    }
22
23    data, _ := os.ReadFile(filepath.Join(dir, "test.txt"))
24    assert.Equal(t, "hello", string(data))
25}
26
27// Cleanup with execution order (LIFO)
28func TestMultipleCleanups(t *testing.T) {
29    t.Cleanup(func() { fmt.Println("Cleanup 1") })
30    t.Cleanup(func() { fmt.Println("Cleanup 2") })
31    t.Cleanup(func() { fmt.Println("Cleanup 3") })
32    // Output: Cleanup 3, Cleanup 2, Cleanup 1 (LIFO)
33}
34
35// t.Setenv: automatic environment variable restoration
36func TestWithEnv(t *testing.T) {
37    t.Setenv("DATABASE_URL", "postgres://localhost/test")
38    // DATABASE_URL is set only for this test
39    // Automatically restored after test
40
41    url := os.Getenv("DATABASE_URL")
42    assert.Equal(t, "postgres://localhost/test", url)
43}