Helpers and cleanup in Go

t.Helper fixes the reported line; t.Cleanup replaces teardown.

func mustEqual(t *testing.T, got, want string) {
    t.Helper() // report the caller's line, not this one
    if got != want {
        t.Fatalf("got %q, want %q", got, want)
    }
}

func TestWithFixture(t *testing.T) {
    dir := t.TempDir()
    path := filepath.Join(dir, "runs.txt")

    if err := os.WriteFile(path, []byte("104\n"), 0o600); err != nil {
        t.Fatalf("write: %v", err)
    }
    t.Cleanup(func() { t.Log("finished with", path) })

    data, err := os.ReadFile(path)
    if err != nil {
        t.Fatalf("read: %v", err)
    }
    mustEqual(t, strings.TrimSpace(string(data)), "104")
}

How it works

1. Without t.Helper, failures point at the helper, not the test.
2. t.Cleanup runs in reverse order after the test.
3. t.TempDir is removed for you when the test ends.

Keywords and builtins used here

• byte
• func
• if
• string

The run, in numbers

Lines

22

Characters to type

536

Tokens

157

Three-star pace

100 tpm

At the three-star pace of 100 tokens a minute, this run takes about 94 seconds.

Type this snippet

Step 3 of 4 in Writing tests, step 3 of 13 in Testing.

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