Test — Module 7: Packages and Modules¶

Topic: [[go]] Module: [[go/7. Packages and Modules]]

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 relationship between a directory and a package in Go? Can a single directory contain two different packages?

Your answer:

1.2 Go has no public or private keywords. What determines whether an identifier (function, type, variable, struct field) is visible outside its package?

Your answer:

1.3 What is the purpose of go.sum? Should it be committed to version control? Can you edit it by hand?

Your answer:

1.4 What does go mod tidy do? Name two situations where you should run it.

Your answer:

1.5 What is the /v2 rule in semantic import versioning? Give a concrete example showing how the import path changes between v1 and v2 of a module.

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 what Minimal Version Selection (MVS) is and why Go uses it instead of "pick the latest compatible version." Consider a scenario where your module requires package A v1.2 (which requires C v1.1) and package B v1.0 (which requires C v1.3). What version of C does MVS select, and why is this better than picking the absolute latest?

Your answer:

2.2 Explain the purpose of the internal/ directory and give a concrete example of when you would use it. What exactly does the Go toolchain enforce — and what does that enforcement look like (compile-time error? Runtime panic? Something else)?

Your answer:

2.3 What problem does go.work (the workspace file) solve? Why is it better than putting a replace directive in go.mod for local multi-module development? Under what condition should go.work NOT be committed to version control?

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 the minimal go.mod file for a module named github.com/myorg/myservice that: - Uses Go 1.22 - Depends on github.com/gin-gonic/gin at exactly version v1.9.1 - Depends on golang.org/x/crypto at version v0.17.0 (this one is an indirect dependency)

Also write the two shell commands you would run to verify the module graph is consistent (no unused or missing dependencies), and to list all modules in the dependency tree.

Your answer:

3.2 Given the following package layout, identify and fix all problems. Explain what each problem is and why it is a problem in Go:

myapp/
  go.mod         — module github.com/myorg/myapp
  util/
    util.go      — package util; contains: DB connection logic, HTTP helpers,
                   string utilities, config loading, email sending
  main.go        — package main; imports util and calls all util functions

// util/util.go
package Util   // ← Problem?

import (
    "database/sql"
    "net/http"
    "fmt"
    "strings"
)

var DB *sql.DB  // global
var Client = &http.Client{}

func connectDB(dsn string) {  // ← Problem?
    // ...
}

func SendEmail(to, subject, body string) error { return nil }
func TrimAndLower(s string) string { return strings.TrimSpace(strings.ToLower(s)) }

Your answer (list at least 3 problems with explanations and fixes):

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 pushes this go.mod to the shared repository:

module github.com/myorg/myservice

go 1.21

require (
    github.com/gin-gonic/gin v1.9.1
    github.com/myorg/mylib v0.3.0
)

replace github.com/myorg/mylib => ../mylib

The CI build fails for every other engineer on the team with:

go: github.com/myorg/mylib@v0.3.0: reading file:///home/runner/../mylib/go.mod:
  open /home/runner/../mylib/go.mod: no such file or directory

Answer all three parts:

a) What is the root cause of the CI failure? Explain precisely why it works on your colleague's machine but fails everywhere else.

b) What is the correct fix? Provide the exact change to make (to which file, and what change).

c) If your colleague needs to continue developing mylib and myapp simultaneously after the fix, what should they do locally?

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 A new Go developer on your team asks: "Why do we have an internal/ directory? If I want something private I'll just not document it — no one will use it." Explain why this reasoning is insufficient and why internal/ provides a stronger guarantee. Consider at least two scenarios where the difference between "convention" and "compiler enforcement" matters in practice.

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 The init() function is powerful but often misused. Consider the following package which uses init() for configuration loading:

package appconfig

import (
    "os"
    "log"
)

var DatabaseURL string
var Port string

func init() {
    DatabaseURL = os.Getenv("DATABASE_URL")
    if DatabaseURL == "" {
        log.Fatal("DATABASE_URL environment variable is required")
    }
    Port = os.Getenv("PORT")
    if Port == "" {
        Port = "8080"
    }
}

Answer all three parts:

a) List at least three specific problems with using init() for this kind of configuration loading.

b) Rewrite this as an explicit initialization function (func Load() (*Config, error)) that solves the problems you identified. Define a Config struct with appropriate fields. The function should return an error (not call log.Fatal) and should not use init() at all.

c) Explain how callers should use your new Load() function — show a main.go that calls it and handles the error correctly.

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.