Go Table Driven Tests

func TestFunctionName(t *testing.T) {
    cases := []struct {
        name  string
        input string
        want  string
        err   error
    }{
        {
            name:  "simple case",
            input: "a/b/c",
            want:  "a,b,c",
        },
        {
            name:  "empty input",
            input: "",
            want:  "",
        },
        {
            name:  "invalid input",
            input: "!!!",
            want:  "",
            err:   ErrInvalid,
        },
    }

    for _, tt := range cases {
        t.Run(tt.name, func(t *testing.T) {
            got, err := FunctionName(tt.input)
            if !errors.Is(err, tt.err) {
                t.Errorf("FunctionName(%q) error = %v, want %v", tt.input, err, tt.err)
            }
            if got != tt.want {
                t.Errorf("FunctionName(%q) = %q, want %q", tt.input, got, tt.want)
            }
        })
    }
}

func TestFunctionName(t *testing.T) {
    tests := map[string]struct {
        input string
        want  string
    }{
        "simple case":   {input: "a/b/c", want: "a,b,c"},
        "empty input":   {input: "", want: ""},
        "trailing sep":  {input: "a/b/c/", want: "a,b,c"},
    }

    for name, tc := range tests {
        t.Run(name, func(t *testing.T) {
            got := FunctionName(tc.input)
            if got != tc.want {
                t.Fatalf("%s: expected %q, got %q", name, tc.want, got)
            }
        })
    }
}

// Always use named fields (not anonymous structs in this codebase)
cases := []struct {
    name      string  // Descriptive test name (REQUIRED when using slice pattern)
    input     Type    // Input to function under test
    want      Type    // Expected output
    err       error   // Expected error (use errors.Is for comparison)
    wantErr   bool    // Alternative: true if error is expected
    precondition func(*testing.T)  // Optional setup function
}{ ... }

// For error checking (preferred)
if !errors.Is(err, tt.err) {
    t.Errorf("error = %v, want %v", err, tt.err)
}

// For simple comparisons
if got != tt.want {
    t.Errorf("got %q, want %q", got, tt.want)
}

// Use t.Fatalf only when continuing doesn't make sense
// Use t.Errorf to see all test failures before stopping

for _, tt := range []struct {
    name         string
    precondition func(*testing.T)
    input        string
    err          error
}{
    {
        name: "with listener",
        precondition: func(t *testing.T) {
            ln, err := net.Listen("tcp", ":8081")
            if err != nil {
                t.Fatal(err)
            }
            t.Cleanup(func() { ln.Close() })
        },
        input: "test",
        err:   nil,
    },
} {
    t.Run(tt.name, func(t *testing.T) {
        if tt.precondition != nil {
            tt.precondition(t)
        }
        // test logic
    })
}

func TestFunctionName(t *testing.T) {
    cases := []struct {
        name  string
        input string
        want  string
    }{
        // ... test cases
    }

    for _, tt := range cases {
        tt := tt // Capture range variable (Go < 1.22)
        t.Run(tt.name, func(t *testing.T) {
            t.Parallel() // Marks this subtest as parallel

            got := FunctionName(tt.input)
            if got != tt.want {
                t.Errorf("got %q, want %q", got, tt.want)
            }
        })
    }
}