Testing package overview in Go - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a simple test function

What is the output when running this Go test code?

Go

package main

import (
	"testing"
)

func TestSum(t *testing.T) {
	sum := 2 + 3
	if sum != 5 {
		t.Errorf("Expected 5 but got %d", sum)
	}
}

func main() {}

A No output because main() is empty

B Compilation error due to missing main function

C

FAIL
--- FAIL: TestSum (0.00s)
    main_test.go:7: Expected 5 but got 6

D

PASS
ok   	command-line-arguments	0.001s

💡 Hint

Tests pass silently unless there is an error.

The test checks if 2 + 3 equals 5, which is true, so the test passes and Go test reports PASS.

❓ Predict Output

intermediate

Behavior of t.Fatal in tests

What happens when t.Fatal is called inside a test function?

Go

package main

import (
	"testing"
)

func TestFailNow(t *testing.T) {
	t.Fatal("Fatal error occurred")
	// This line will not run
	t.Log("This will not print")
}

func main() {}

A Test fails immediately and logs the fatal message; subsequent lines are skipped.

B Test logs the fatal message but continues running the rest of the test.

C Test passes because t.Fatal only logs a message.

D Compilation error because t.Fatal cannot be called directly.

💡 Hint

t.Fatal stops the test immediately after logging.

t.Fatal logs the message and stops the test immediately, so lines after it do not run.

❓ Predict Output

advanced

Output of a benchmark function

What output does this benchmark produce when run with 'go test -bench=.'?

Go

package main

import (
	"testing"
)

func BenchmarkLoop(b *testing.B) {
	for i := 0; i < b.N; i++ {
		_ = i * i
	}
}

func main() {}

A

goos: linux
goarch: amd64
BenchmarkLoop-8    1000000000               1.23 ns/op
PASS

B

BenchmarkLoop-8    1000000000               1.23 ms/op
FAIL

C No output because main() is empty

D Compilation error due to missing testing import

💡 Hint

Benchmarks report number of iterations and time per operation.

The benchmark runs b.N times and reports ns/op; the test passes if no error occurs.

❓ Predict Output

advanced

Effect of t.Skip in a test

What is the output when t.Skip is called inside a test function?

Go

package main

import (
	"testing"
)

func TestSkipExample(t *testing.T) {
	t.Skip("Skipping this test")
	t.Error("This error will not be reported")
}

func main() {}

A

--- FAIL: TestSkipExample (0.00s)
    main_test.go:8: This error will not be reported
FAIL

B

--- SKIP: TestSkipExample (0.00s)
    main_test.go:7: Skipping this test
PASS

C Test runs normally and reports no skip or fail

D Compilation error due to t.Skip usage

💡 Hint

t.Skip stops the test and marks it as skipped.

t.Skip stops the test immediately and marks it as skipped; errors after it are ignored.

🧠 Conceptual

expert

Understanding parallel tests with t.Parallel

Which statement best describes the behavior of tests that call t.Parallel() in Go?

A Tests calling t.Parallel() run concurrently and immediately without waiting for any other tests.

B Tests calling t.Parallel() run sequentially after all non-parallel tests complete.

C Tests calling t.Parallel() run concurrently with other parallel tests but wait for the parent test to finish.

D Tests calling t.Parallel() cause the test suite to fail if run in parallel.

💡 Hint

Parallel tests run concurrently but respect the parent test's lifecycle.

t.Parallel marks the test to run concurrently with other parallel tests but waits for the parent test function to complete before finishing.

Practice

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

easy

A. To compile Go programs faster

B. To create graphical user interfaces

C. To manage database connections

D. To write functions that check if your code works correctly

Solution

1. Step 1: Understand the role of the testing package

   The testing package is designed to help write tests that verify code correctness.

2. Step 2: Identify the correct purpose

   It does not handle GUIs, databases, or compilation speed but focuses on testing functions.

3. Final Answer:

   To write functions that check if your code works correctly -> Option D

4. Quick Check:

   testing package = write test functions [OK]

Hint: Testing package is for checking code correctness [OK]

Common Mistakes:

• Confusing testing with UI or database packages
• Thinking it speeds up compilation
• Assuming it manages runtime behavior

2. Which of the following is the correct way to name a test function in Go using the testing package?

easy

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

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

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

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

Solution

1. Step 1: Recall test function naming rules

   Test functions must start with uppercase 'Test' followed by the function name.

2. Step 2: Match the correct naming pattern

   Only func TestMyFunction(t *testing.T) {} uses 'Test' prefix correctly and has the right signature.

3. Final Answer:

   func TestMyFunction(t *testing.T) {} -> Option A

4. Quick Check:

   Test functions start with 'Test' [OK]

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

Common Mistakes:

• Starting function name with lowercase 'test'
• Placing 'Test' at the end of the function name
• Using incorrect function signature

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

package main

import "testing"

func TestSum(t *testing.T) {
  total := 2 + 3
  if total != 5 {
    t.Error("Sum was incorrect")
  }
}

medium

A. Syntax error: missing return type

B. FAIL
Sum was incorrect

C. PASS
ok main 0.001s

D. No tests to run

Solution

1. Step 1: Analyze the test logic

   The test calculates 2 + 3 and checks if it equals 5, which is true, so no error is called.

2. Step 2: Understand test output

   Since the test passes, go test reports PASS with timing info.

3. Final Answer:

   PASS ok main 0.001s -> Option C

4. Quick Check:

   Correct test = PASS output [OK]

Hint: If no t.Error called, test passes [OK]

Common Mistakes:

• Assuming test fails without error call
• Confusing syntax errors with test failures
• Expecting output when no tests exist

4. Identify the error in this test function:

package main

import "testing"

func TestMultiply(t *testing.T) {
  result := 3 * 4
  if result = 12 {
    t.Log("Multiplication correct")
  }
}

medium

A. t.Log cannot be used inside tests

B. Using assignment '=' instead of comparison '==' in if condition

C. Test function name should be lowercase

D. Missing import of fmt package

Solution

1. Step 1: Check the if condition syntax

   The condition uses '=' which assigns value instead of '==' which compares values.

2. Step 2: Understand Go syntax rules

   Using '=' in if condition causes a compile error; '==' is needed for comparison.

3. Final Answer:

   Using assignment '=' instead of comparison '==' in if condition -> Option B

4. Quick Check:

   Use '==' for comparison in if [OK]

Hint: Use '==' for comparisons, not '=' [OK]

Common Mistakes:

• Confusing assignment '=' with equality '=='
• Thinking t.Log is disallowed
• Ignoring function naming conventions

5. You want to write a test that fails if a function returns an empty string. Which of these test snippets correctly uses the testing package to do this?

func TestNonEmpty(t *testing.T) {
  result := getName()
  // Which check is correct?
}

hard

A. if result == "" { t.Error("Result should not be empty") }

B. if result != "" { t.Error("Result should not be empty") }

C. if result == nil { t.Error("Result should not be empty") }

D. if result == 0 { t.Error("Result should not be empty") }

Solution

1. Step 1: Understand the test goal

   The test must fail if the returned string is empty, so check if result equals empty string.

2. Step 2: Choose the correct condition

   if result == "" { t.Error("Result should not be empty") } checks if result == "" and calls t.Error, which correctly fails the test on empty string.

3. Final Answer:

   if result == "" { t.Error("Result should not be empty") } -> Option A

4. Quick Check:

   Fail test when string is empty [OK]

Hint: Check empty string with == "" to fail test [OK]

Common Mistakes:

• Using != instead of == for empty check
• Comparing string to nil or 0
• Not calling t.Error on failure condition