Test — Module 11: Testing and Benchmarking¶

Topic: [[go]] Module: [[go/11. Testing and Benchmarking]]

Before You Begin¶

[!WARNING] Do not look at ANSWERS.md or your notes during the test. The purpose of this test is to surface what you truly know vs. what you think you know. An inflated score is worthless. An honest score shows you exactly where to focus next.

Instructions: 1. Close all notes, the module README, and any reference materials. 2. Set a timer. Note your start time below. 3. Attempt every question — partial credit exists. 4. After finishing, grade yourself using ANSWERS.md. 5. Record your score in the Grading Record at the bottom.

Start time: ___________ End time: ___________ Total time: ___________

Scoring Table¶

Passing score: 15/22 (68%)  ·  Target score: 18/22 (82%)

Section 1: Recall (5 questions × 1 pt = 5 pts)¶

Quick recall questions. Answer from memory in 1–3 sentences each.

1.1 What is the difference between t.Error/t.Errorf and t.Fatal/t.Fatalf? Give one example of when you would choose t.Fatal over t.Error.

Your answer:

1.2 What does b.N represent in a Go benchmark function? Who sets its value, and why should you never set it yourself?

Your answer:

1.3 What flag do you pass to go test to run only tests whose names match a pattern? Write the command to run only tests whose names contain "Parse".

Your answer:

1.4 What is t.Helper() and why is it important to call it at the start of test helper functions?

Your answer:

1.5 What is the naming convention for Go test files and test functions? Name the three function signature conventions for the three types of automated tests (unit test, benchmark, fuzz test).

Your answer:

Section 2: Conceptual Understanding (3 questions × 2 pts = 6 pts)¶

Demonstrate that you understand the "why", not just the "what".

2.1 Explain why Go's community prefers hand-written fakes over mock frameworks (like gomock or testify/mock). What role do Go's interfaces play in making fakes practical? Reference the concept of structural typing in your answer.

Your answer:

2.2 Explain the loop variable capture bug in parallel table-driven tests (pre-Go 1.22). Why does it happen, what symptom does it cause, and what is the fix?

Your answer:

2.3 What is the difference between running a fuzz test with go test -run FuzzXxx versus go test -fuzz FuzzXxx? What happens in each case, and when would you use each?

Your answer:

Section 3: Applied / Practical (2 questions × 3 pts = 6 pts)¶

Show that you can use your knowledge to solve real problems.

3.1 Write a complete, idiomatic table-driven test for the following function. Your test must include at least 4 cases, use t.Run subtests, and follow the wantErr bool pattern for error checking:

func Sqrt(x float64) (float64, error) {
    if x < 0 {
        return 0, fmt.Errorf("sqrt of negative number: %v", x)
    }
    return math.Sqrt(x), nil
}

Your answer:

3.2 Write a benchmark for the following two implementations. Ensure that the setup (building the input map) is not included in the ns/op measurement. Add a comment explaining which implementation you would expect to be faster and why.

// LookupSlice searches for key in a slice of key-value pairs.
func LookupSlice(pairs [][2]string, key string) (string, bool) {
    for _, p := range pairs {
        if p[0] == key {
            return p[1], true
        }
    }
    return "", false
}

// LookupMap looks up key in a map.
func LookupMap(m map[string]string, key string) (string, bool) {
    v, ok := m[key]
    return v, ok
}

Use 1000 key-value pairs and look up a key that exists near the middle of the collection.

Your answer:

Section 4: Scenario / Debugging (1 question × 3 pts = 3 pts)¶

Analyze a realistic scenario and identify what's wrong or what should be done.

4.1 A colleague wrote the following benchmark, but the results seem unreliable — sometimes showing 0 ns/op. Identify what is wrong, explain why it produces incorrect results, and rewrite it correctly.

func BenchmarkProcessItems(b *testing.B) {
    for i := 0; i < b.N; i++ {
        items := generateItems(1000) // expensive setup — takes ~10ms
        result := ProcessItems(items)
        _ = result
    }
}

a) What is wrong with this benchmark?

b) Why does it produce incorrect or misleading results?

c) Rewrite it correctly.

Your answer:

Section 5: Essay / Discussion (1 question × 2 pts = 2 pts)¶

Open-ended. There is more than one good answer. Show your reasoning.

5.1 "Go's testing package deliberately provides no assertion library — no assertEqual, no assertNotNil, no assertContains. This is a design decision, not an omission."

Do you agree? Explain why this design decision might be justified, what its trade-offs are, and what you gain or lose compared to using a library like testify/assert. Consider what happens when a test fails in each approach.

Your answer (aim for 3–6 sentences):

Section 6: Bonus Challenge (1 question × +5 pts)¶

[!NOTE] This question is optional. It will not count against you if you skip it or get it wrong. Only attempt it after completing Sections 1–5.

6.1 Write a complete fuzz test for the following base64 codec — one that checks both directions of the round-trip: encode then decode, and also decode then encode (where the input is valid base64).

func Encode(data []byte) string {
    return base64.StdEncoding.EncodeToString(data)
}

func Decode(s string) ([]byte, error) {
    return base64.StdEncoding.DecodeString(s)
}

Your fuzz test must: 1. Use f.Add([]byte(...)) seed entries (including an empty slice) 2. Assert the round-trip invariant: Decode(Encode(data)) must return data equal to the original 3. Assert that Encode never returns an empty string for non-empty input 4. Handle the case where Decode is called with arbitrary strings (most will be invalid base64)

Explain which invariant is most likely to find bugs in a real implementation of this codec.

Your answer:

Self-Assessment¶

After grading your test, answer these questions honestly:

What did I get right and why?

Your reflection:

What did I get wrong and why did I make that mistake?

Your reflection:

What should I review before moving to the next module?

Your reflection:

What score did I get? Do I feel it accurately reflects my understanding?

Your reflection:

Grading Record¶

Append a new row each time you take this test. Do not overwrite previous attempts.

Grade scale: A ≥ 90% (≥20/22)  ·  B ≥ 80% (≥18/22)  ·  C ≥ 70% (≥15/22)  ·  D ≥ 60% (≥13/22)  ·  F < 60%

See ANSWERS.md for the answer key. Review it only after completing the test.