Test — Module 8: Error Handling¶

Topic: [[go]] Module: [[go/8. Error Handling]]

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 definition of the error interface in Go? Write it out exactly (or as close as you can from memory).

Your answer:

1.2 What is the difference between fmt.Errorf("context: %v", err) and fmt.Errorf("context: %w", err)? When would you choose each?

Your answer:

1.3 What does errors.Is(err, target) do that a direct err == target comparison does not?

Your answer:

1.4 What is errors.Join used for, and in which Go version was it added?

Your answer:

1.5 Inside what kind of function must recover() be called for it to actually stop a panic? What happens if you call recover() outside that context?

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 the "typed-nil error trap." What is it, why does it happen, and how do you avoid it? Include a concrete code example showing the wrong version and the correct version.

Your answer:

2.2 Go uses errors-as-values rather than exceptions. Give two concrete advantages of the errors-as-values approach for a professional engineer reading or debugging a large codebase. Avoid vague claims like "it's simpler" — be specific about what is easier or harder in each model.

Your answer:

2.3 Explain the difference between errors.Is and errors.As. When would you use each? Give one scenario where errors.Is is the right tool and one scenario where errors.As is the right tool.

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 Go function openDB(dsn string) (*sql.DB, error) that: - Opens a database connection using sql.Open("postgres", dsn) - Pings the database using db.Ping() - Returns the *sql.DB on success - Wraps any error with appropriate context using fmt.Errorf and %w

You do not need to write an import block or make it compile — focus on the function body and error handling idioms.

Your answer:

3.2 Write a Go function safeEval(expr string, eval func(string) int) (result int, err error) that: - Uses named return values - Defers a function that recovers from any panic, converting it to an error via err = fmt.Errorf("safeEval: panic: %v", r) - Calls eval(expr) and returns its result - Returns 0, nil if eval succeeds without panicking

Show the function signature and body only — you do not need a full program.

Your answer:

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

Analyze a realistic scenario and identify what's wrong.

4.1 The following code has three distinct error handling problems. Identify each one, explain why it is a problem, and describe the correct fix.

func processRequest(userID int) (User, error) {
    var fetchErr *FetchError
    u, err := fetchUser(userID)
    if err != nil {
        log.Printf("fetchUser failed: %v", err)
        return User{}, err
    }

    data, err := loadProfile(u.ProfileID)
    if err != nil {
        if err == ErrNotFound {  // direct == comparison
            return User{}, ErrNotFound
        }
        return User{}, err  // bare return, no context
    }

    return buildUser(u, data), fetchErr  // returns fetchErr which is always nil
}

For each problem: name it, explain why it is wrong, and write the corrected line or block.

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 "Use panic only for programmer errors and unrecoverable situations — never for expected failure modes." Explain what this guideline means in practice. Give one example of a situation where panic is appropriate and one where it is not. For the inappropriate case, describe the correct alternative. Also explain: what makes a situation "expected" vs. "unrecoverable"?

Your answer (aim for 4–7 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 Design and implement a Result[T] type in Go that encapsulates either a value or an error — similar to Rust's Result<T, E> or Haskell's Either. Your implementation must:

1. Define type Result[T any] struct with appropriate fields (Go 1.18+ generics)
2. Provide OK(v T) Result[T] and Err(e error) Result[T] constructors
3. Provide func (r Result[T]) Unwrap() (T, error) — returns the value or error
4. Provide func (r Result[T]) Must() T — returns the value or panics if it's an error
5. Write a brief explanation of when this abstraction is useful and when idiomatic Go (T, error) returns are preferable

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.