Standard Library

Go ships with one of the most capable standard libraries of any language. From HTTP servers to JSON encoding to a full testing framework -- most Go programs need few external dependencies. This section covers the packages you'll use daily.

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#	Topic	What You'll Learn	Level
1	Input & Output	fmt verbs, os.Stdin/Stdout, bufio.Scanner, format strings	Beginner
2	File I/O & OS Operations	Read/write files, filepath.WalkDir, temp files, env vars	Intermediate
3	JSON & XML Encoding	Marshal/unmarshal, struct tags, streaming, json.RawMessage	Intermediate
4	HTTP Client & Server	net/http, handlers, middleware, Go 1.22 routing, graceful shutdown	Intermediate
5	Error Wrapping & Custom Errors	%w, errors.Is, errors.As, error chains, custom types	Intermediate
6	Defer, Panic & Recover	LIFO order, cleanup patterns, recovery middleware	Intermediate
7	Closures & Anonymous Functions	Variable capture, loop gotcha, middleware pattern	Intermediate
8	Go Modules & Dependencies	go.mod, versioning, MVS algorithm, vendoring, workspaces	Intermediate
9	Unit Testing	Table-driven tests, subtests, t.Helper(), coverage	Intermediate
10	Advanced Testing	Mocks, fuzz testing, integration tests, golden files, benchmarks	Advanced

Interview Quick Hits

• Go's net/http is production-grade -- no framework needed for most services
• Table-driven tests are THE Go testing pattern -- every interviewer expects them
• errors.Is walks the error chain; errors.As extracts typed errors -- know both
• Defer runs in LIFO order; arguments are evaluated at the defer statement, not when executed
• Go modules use Minimum Version Selection (MVS) -- unique among package managers
• Go 1.22 added method+pattern routing: mux.HandleFunc("GET /users/{id}", handler)