Test-driven basics in Go - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a simple test function

What will be the output when running this Go test code with go test?

Go

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")
    }
}

A No output, test file not recognized

B

FAIL
--- FAIL: TestAdd (0.00s)
    main_test.go:9: Expected 5

C panic: runtime error: invalid memory address or nil pointer dereference

D

PASS
ok  	command-line-arguments	0.001s

💡 Hint

The test checks if Add(2, 3) equals 5 and calls t.Error only if it doesn't.

The function Add correctly returns the sum of 2 and 3, which is 5, so the test passes without errors.

❓ Predict Output

intermediate

Test failure output

What output will this test produce when run with go test?

Go

package main

import "testing"

func Multiply(a, b int) int {
    return a * b
}

func TestMultiply(t *testing.T) {
    if Multiply(2, 3) != 6 {
        t.Error("Expected 6")
    }
    if Multiply(2, 0) != 0 {
        t.Error("Expected 0")
    }
    if Multiply(2, -1) != -2 {
        t.Error("Expected -2")
    }
    if Multiply(2, 2) != 5 {
        t.Error("Expected 5")
    }
}

A

FAIL
--- FAIL: TestMultiply (0.00s)
    main_test.go:15: Expected 5

B

PASS
ok  	command-line-arguments	0.001s

C

FAIL
--- FAIL: TestMultiply (0.00s)
    main_test.go:9: Expected 6

D panic: index out of range

💡 Hint

Look carefully at the last if condition and its expected value.

The last condition expects Multiply(2, 2) to be 5, but it returns 4, so the test fails with that error.

🔧 Debug

advanced

Identify the test bug causing no tests to run

Why does this test file produce 'ok command-line-arguments 0.001s' without running any tests?

Go

package main

import "testing"

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

func testAdd(t *testing.T) {
    if add(1, 2) != 3 {
        t.Error("Expected 3")
    }
}

A The test function name must start with uppercase 'Test' to be recognized by go test.

B The add function is unexported and cannot be tested.

C The testing package is not imported correctly.

D The package name must be 'main_test' for tests to run.

💡 Hint

Test functions must follow a naming convention to be detected.

Go test only runs functions starting with 'Test' and taking *testing.T as parameter. 'testAdd' is ignored.

📝 Syntax

advanced

Syntax error in test function

Which option contains the correct syntax for a Go test function?

A

func testSum(t *testing.T) {
    if Sum(1, 2) != 3 {
        t.Error("fail")
    }
}

B

func TestSum() {
    if Sum(1, 2) != 3 {
        t.Error("fail")
    }
}

C

func TestSum(t *testing.T) {
    if Sum(1, 2) != 3 {
        t.Error("fail")
    }
}

D

func TestSum(t testing.T) {
    if Sum(1, 2) != 3 {
        t.Error("fail")
    }
}

💡 Hint

Test functions must be exported and accept *testing.T as parameter.

Only option C has the correct function name and parameter type for a Go test function.

🚀 Application

expert

Number of tests run in a file

Given this test file, how many tests will be executed when running go test?

Go

package main

import "testing"

func TestOne(t *testing.T) {}
func TestTwo(t *testing.T) {}
func TestThree(t *testing.T) {}
func testFour(t *testing.T) {}
func TestFive() {}
func TestSix(t testing.T) {}

A 4

B 3

C 5

D 6

💡 Hint

Only functions starting with 'Test', exported, and with *testing.T parameter run as tests.

Only TestOne, TestTwo, and TestThree meet all criteria. Others fail naming or signature rules.