Test-driven basics in Go

Introduction

Test-driven basics help you write code that works right the first time. You write tests before the code to check if it does what you want.

When you want to make sure your code does exactly what you expect.

When you want to catch mistakes early before running the full program.

When you want to add new features safely without breaking old ones.

When you want to understand the requirements clearly before coding.

Syntax

Go

func TestFunctionName(t *testing.T) {
    // test code here
}

Test functions start with Test and take *testing.T as a parameter.

Use t.Error or t.Fatal to report test failures.

Examples

This test checks if the Add function returns 5 when adding 2 and 3.

Go

func TestAdd(t *testing.T) {
    got := Add(2, 3)
    want := 5
    if got != want {
        t.Errorf("Add(2, 3) = %d; want %d", got, want)
    }
}

This test checks if IsEven correctly identifies even and odd numbers.

Go

func TestIsEven(t *testing.T) {
    if !IsEven(4) {
        t.Error("4 should be even")
    }
    if IsEven(5) {
        t.Error("5 should not be even")
    }
}

Sample Program

This program defines a simple Add function.

You run the test using go test command in the terminal.

Go

package main

func Add(a, b int) int {
    return a + b
}

// To run this test, save the test code in a separate file named add_test.go
// and run: go test

Important Notes

Test files in Go end with _test.go and are separate from main code files.

Run tests with go test in the terminal inside your project folder.

Tests help you find bugs early and keep your code working as you add features.

Summary

Write tests before or alongside your code to check it works.

Test functions start with Test and use *testing.T to report errors.

Run tests with go test to see if your code passes or fails.

Practice

1. What is the main purpose of writing tests in Go using the testing package?

easy

A. To make the program run faster

B. To add comments to the code

C. To check if the code works correctly by running test functions

D. To create user interfaces

Solution

1. Step 1: Understand the role of tests in Go

   Tests are written to verify that the code behaves as expected.

2. Step 2: Identify what the testing package does

   The testing package provides tools to write and run tests that check code correctness.

3. Final Answer:

   To check if the code works correctly by running test functions -> Option C

4. Quick Check:

   Tests check code correctness = B [OK]

Hint: Tests verify code correctness before running fully [OK]

Common Mistakes:

• Thinking tests improve speed
• Confusing tests with comments
• Assuming tests create UI

2. Which of the following is the correct way to start a test function in Go?

easy

A. func testMyFunc(t *testing.T) {}

B. func MyFuncTest(t *testing.T) {}

C. func TestingMyFunc(t *testing.T) {}

D. func TestMyFunc(t *testing.T) {}

Solution

1. Step 1: Recall Go test function naming rules

   Test functions must start with "Test" and take a *testing.T parameter.

2. Step 2: Match the correct function signature

   Only func TestMyFunc(t *testing.T) {} follows this rule exactly.

3. Final Answer:

   func TestMyFunc(t *testing.T) {} -> Option D

4. Quick Check:

   Test functions start with "Test" = C [OK]

Hint: Test functions must start with uppercase 'Test' [OK]

Common Mistakes:

• Starting function name with lowercase 'test'
• Adding extra words before 'Test'
• Using wrong parameter types

3. What will be the output when running go test on this test file?

package main

import "testing"

func Add(a, b int) int {
    return a + b
}

func TestAdd(t *testing.T) {
    if Add(2, 3) != 5 {
        t.Error("Expected 5")
    }
}

medium

A. No output

B. PASS

C. Compilation error

D. FAIL with error 'Expected 5'

Solution

1. Step 1: Analyze the Add function and test

   The Add function returns the sum of 2 and 3, which is 5.

2. Step 2: Check the test condition

   The test expects Add(2, 3) to be 5, which is true, so no error is called.

3. Final Answer:

   PASS -> Option B

4. Quick Check:

   Correct sum means test passes = D [OK]

Hint: If test condition matches, output is PASS [OK]

Common Mistakes:

• Assuming test fails when condition is true
• Thinking test prints 'Expected 5' on success
• Confusing test failure with compile error

4. Identify the error in this test code snippet:

package main

import "testing"

func TestMultiply(t *testing.T) {
    result := Multiply(2, 3)
    if result != 6 {
        t.Error("Expected 6")
    }
}

medium

A. Multiply function is not defined

B. Missing import for Multiply function

C. Test function name should be lowercase

D. t.Error should be t.Fail

Solution

1. Step 1: Check if Multiply function is defined

   The code snippet does not show any definition or import of Multiply function.

2. Step 2: Understand Go requires functions to be defined or imported

   Without definition or import, the code will not compile.

3. Final Answer:

   Multiply function is not defined -> Option A

4. Quick Check:

   Undefined function causes compile error = A [OK]

Hint: Undefined functions cause compile errors [OK]

Common Mistakes:

• Thinking test function names can be lowercase
• Confusing t.Error with t.Fail
• Assuming missing import causes runtime error

5. You want to write a test that fails if a function returns an empty string. Which test code snippet correctly implements this check?

hard

A. func TestEmpty(t *testing.T) {
if MyFunc() == "" {
t.Error("Result should not be empty")
}
}

B. func TestEmpty(t *testing.T) {
if MyFunc() != "" {
t.Error("Result should be empty")
}
}

C. func TestEmpty(t *testing.T) {
if MyFunc() == nil {
t.Error("Result should not be nil")
}
}

D. func TestEmpty(t *testing.T) {
if MyFunc() == 0 {
t.Error("Result should not be zero")
}
}

Solution

1. Step 1: Understand the test goal

   The test should fail if the function returns an empty string "".

2. Step 2: Check each option's condition

   func TestEmpty(t *testing.T) { if MyFunc() == "" { t.Error("Result should not be empty") } } fails when MyFunc() returns "", which matches the goal.

3. Final Answer:

   func TestEmpty(t *testing.T) { if MyFunc() == "" { t.Error("Result should not be empty") } } -> Option A

4. Quick Check:

   Fail on empty string = A [OK]

Hint: Fail test if function returns empty string "" [OK]

Common Mistakes:

• Checking for nil instead of empty string
• Checking for zero instead of string
• Reversing the condition logic