3.6 Table-Driven Tests | Errors, Testing & Confidence | Infrastructure Development with Go

The Go testing idiom. Instead of writing separate functions for each case, define a table:

2 · Worked example — read every step

func TestParsePort(t *testing.T) {
    tests := []struct {
        name    string
        input   string
        want    int
        wantErr bool
    }{
        {name: "valid port", input: "8080", want: 8080},
        {name: "port 1", input: "1", want: 1},
        {name: "port 65535", input: "65535", want: 65535},
        {name: "zero", input: "0", wantErr: true},
        {name: "negative", input: "-1", wantErr: true},
        {name: "too high", input: "70000", wantErr: true},
        {name: "not a number", input: "abc", wantErr: true},
        {name: "empty string", input: "", wantErr: true},
    }

    for _, tt := range tests {
        t.Run(tt.name, func(t *testing.T) {
            got, err := ParsePort(tt.input)
            if tt.wantErr {
                if err == nil {
                    t.Errorf("expected error, got nil")
                }
                return
            }
            if err != nil {
                t.Fatalf("unexpected error: %v", err)
            }
            if got != tt.want {
                t.Errorf("got %d, want %d", got, tt.want)
            }
        })
    }
}

Why this pattern is powerful:

Adding a test case is one line
Each case runs as a subtest (t.Run) — failures show which case failed
Easy to test error cases alongside happy paths
go test -run TestParsePort/zero runs just one case

3 · Fill the gaps

The skeleton of every table test you'll write, from memory.

tests := []struct {
    name    string
    input   string
    want    int
    wantErr bool
}{
    {name: "valid port", input: "8080", want: 8080},
    {name: "zero", input: "0", },
}

for _, tt := range tests {
    t.Run(, func(t *testing.T) {
        got, err := ParsePort(tt.input)
        if  {
            if err == nil {
                t.Errorf("expected error, got nil")
            }
            
        }
        if got != tt.want {
            t.Errorf("got %d, want %d", got, tt.want)
        }
    })
}

Python comparison

# Python: @pytest.mark.parametrize("input,expected", [...])
# Go: same idea, but it's just a struct slice + loop. No framework needed.

4 · From scratch — this feeds your review queue