Test-driven basics in Go - Mini Project: Build & Apply

Test-driven basics

📖 Scenario: You are building a simple calculator function in Go. You will write the function step-by-step using test-driven development (TDD). This means you will first write tests that describe what the function should do, then write the function code to pass those tests.

🎯 Goal: Create a Go function called Add that takes two integers and returns their sum. You will write tests first, then write the function to pass those tests.

📋 What You'll Learn

Create a test function called TestAdd in a file named main_test.go.

Write a test case inside TestAdd that checks if Add(2, 3) returns 5.

Create the Add function in main.go that takes two int parameters and returns their sum.

Run the test to confirm it passes and print the result.

💡 Why This Matters

🌍 Real World

Writing tests before code helps catch mistakes early and ensures your code works as expected.

💼 Career

Test-driven development (TDD) is a common practice in software engineering jobs to improve code quality and reliability.

1

Write the test function

Create a test function called TestAdd in main_test.go. Inside it, use t.Errorf to fail the test with the message "Test not implemented". This sets up the test file.

Go

// main_test.go
package main

import "testing"

func TestAdd(t *testing.T) {
    // Your code here
}

Hint

Remember to import the testing package and define TestAdd with t *testing.T parameter.

2

Write the test case for Add(2, 3)

In TestAdd, write a test case that calls Add(2, 3) and checks if the result equals 5. Use if and t.Errorf to report failure with message "Add(2, 3) = %d; want 5".

Go

package main

import "testing"

func TestAdd(t *testing.T) {
    // Your code here
}

Hint

Call Add(2, 3) and compare the result to 5. Use t.Errorf to show an error if they don't match.

3

Write the Add function

Create the Add function in main.go. It should take two int parameters named a and b, and return their sum as an int.

Go

package main

// Your code here

import "testing"

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

Hint

Define Add with two int inputs and return their sum.

4

Run the test and print success message

Run the test using go test. Then add a main function in main.go that calls Add(2, 3) and prints the result using fmt.Println.

Go

package main

import "fmt"

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

func main() {
    // Your code here
}

import "testing"

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

Hint

Use fmt.Println to print the result of Add(2, 3) in main.

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