Test Helpers

In this lesson, explore test helpers through one small Go program, and connect its output to the language rules behind it.

Use helper functions to remove repeated test setup and assertions. Call t.Helper() inside a helper so error reports point to the calling test line instead of the helper implementation.

Keep helpers small enough that expected behavior stays visible. A helper should simplify a test, not hide its main assertion.

Follow this diagram before executing the example. Check where a value or decision changes what runs next.

Helper in a test file

package main
import "testing"
func assertInt(t *testing.T, got, want int) {
    t.Helper()
    if got != want { t.Errorf("got %d; want %d", got, want) }
}
func TestMultiply(t *testing.T) { assertInt(t, multiply(3, 4), 12) }

This example is a complete program. Save it as main.go or paste it into the Go Playground.

Go code

package main

import "fmt"

func multiply(a, b int) int          { return a * b }
func expectEqual(got, want int) bool { return got == want }
func main() {
	fmt.Println("Case good:", expectEqual(multiply(3, 4), 12))
}

Output

Case good: true

The sample separates calculation from the repeated equality check. An actual test helper receives *testing.T and reports a failure through it.

• Calling t.Helper matters for useful file and line numbers.
• Test helpers should use t.Fatal only when continuing would invalidate the test.

Write assertEqual(t, got, want) using t.Helper and t.Errorf, then use it twice.

Tip: Edit the example above, predict the output, and run the modified code to test your reasoning.

You have practiced Test Helpers in a small, self-contained program. The important habit is to predict what runs, inspect the actual output and distinguish the language rule from the particular example.

Before continuing, make sure you can explain the program to someone who has not seen it, including the line that changes its result.