What are table-driven tests in Go and why are they the preferred testing pattern?

Table-driven tests define multiple test cases as a slice of structs, then iterate over them running each case. This is Go's idiomatic testing pattern — it reduces duplication, makes it easy to add new cases, and provides clear failure messages identifying which case failed.

func divide(a, b float64) (float64, error) {
    if b == 0 {
        return 0, errors.New("division by zero")
    }
    return a / b, nil
}

func TestDivide(t *testing.T) {
    tests := []struct {
        name     string
        a, b     float64
        want     float64
        wantErr  bool
    }{
        {name: "positive division",    a: 10, b: 2, want: 5, wantErr: false},
        {name: "negative result",      a: -6, b: 3, want: -2, wantErr: false},
        {name: "division by zero",     a: 5,  b: 0, want: 0,  wantErr: true},
        {name: "float division",       a: 7,  b: 2, want: 3.5, wantErr: false},
    }

    for _, tt := range tests {
        t.Run(tt.name, func(t *testing.T) {
            got, err := divide(tt.a, tt.b)

            if (err != nil) != tt.wantErr {
                t.Errorf("divide(%v, %v) error = %v, wantErr = %v",
                    tt.a, tt.b, err, tt.wantErr)
                return
            }
            if !tt.wantErr && got != tt.want {
                t.Errorf("divide(%v, %v) = %v, want %v",
                    tt.a, tt.b, got, tt.want)
            }
        })
    }
}

// Run specific subtests: go test -run TestDivide/division_by_zero
// Parallel subtests:
for _, tt := range tests {
    tt := tt // capture range var (pre-Go 1.22)
    t.Run(tt.name, func(t *testing.T) {
        t.Parallel()  // run subtests in parallel
        // ...
    })
}

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