Testing Go

Go Testing

Target: $ARGUMENTS

Writes focused, behavior-driven tests following project testing strategy.

Quick Reference

TDD methodology (language-agnostic): See tdd-core plugin (testing-tdd skill)

Go-specific documentation: references/

• references/testing-strategy.md — Go tools (go test, testify, rapid, gomock)
• references/tdd-best-practices.md — Go TDD examples (extends tdd-core)

Quick Decision

go test (default): Use table-driven tests for known cases. Works at unit/integration levels.

rapid (edge cases): Use for invariants that must hold for ALL inputs.

See references/testing-strategy.md for full methodology comparison.

TDD Essentials (Quick Reference)

Cycle: RED (failing test / compile error) -> GREEN (minimal pass) -> REFACTOR (clean up)

Structure: Arrange-Act-Assert (AAA)

func TestOrderCalculator_Total_SumsItemPrices(t *testing.T) {
    // ARRANGE
    calc := NewOrderCalculator()
    items := []Item{{Price: 10.00, Qty: 2}, {Price: 5.00, Qty: 1}}

    // ACT
    total := calc.Total(items)

    // ASSERT
    assert.Equal(t, 25.00, total)
}

Table-Driven Tests (Go Idiom)

func TestValidateEmail(t *testing.T) {
    tests := []struct {
        name    string
        email   string
        wantErr bool
    }{
        {name: "valid", email: "user@example.com", wantErr: false},
        {name: "missing @", email: "userexample.com", wantErr: true},
        {name: "empty", email: "", wantErr: true},
    }
    for _, tt := range tests {
        t.Run(tt.name, func(t *testing.T) {
            err := ValidateEmail(tt.email)
            if tt.wantErr {
                require.Error(t, err)
            } else {
                require.NoError(t, err)
            }
        })
    }
}

What to Test (KISS/DRY/YAGNI)

High-Value: Business logic, error paths, integration points, contracts

Avoid: Stdlib behavior, trivial getters, default zero values, type existence

See references/testing-strategy.md -> "Patterns to Remove" for full list.

Naming Convention

Format: Test{Type}_{Method}_{Behavior}

TestUserService_Create_ReturnsIDOnSuccess
TestValidateEmail_MissingAt
TestCalculateTotal_EmptyItems

Execution

go test ./...                           # All tests
go test -run TestUserService ./...      # Filter by name
go test -race ./...                     # Race detector
go test -v -run TestValidateAge ./...   # Verbose single test

Quality Gates

• All tests pass (go test ./...)
• TDD Red-Green-Refactor followed
• Arrange-Act-Assert structure used
• Table-driven tests for multiple cases
• Behavior-focused (not implementation)
• No stdlib behavior tested
• Interface fakes use var _ Interface = (*fake)(nil) compile check