Table-driven tests
- Go course
- Intermediate
- Lesson 43/80
- 4 min
Learn the table-driven test pattern.
Table-driven tests
Go's most common test pattern: keep inputs and expected outputs in a slice and try them in one loop.
tests := []struct {
ad string
a, b int
want int
}{
{"pozitif", 2, 3, 5},
{"negatif", -2, -3, -5},
{"sıfır", 0, 0, 0},
}
for _, tt := range tests {
t.Run(tt.ad, func(t *testing.T) {
if got := Topla(tt.a, tt.b); got != tt.want {
t.Errorf("got %d, want %d", got, tt.want)
}
})
}Adding a case is cheap
When a bug is reported, a new row that catches it is added to the table; the test code doesn't change. The table is a good checklist so edge cases (empty input, boundary values, Unicode) aren't forgotten. go test -run 'TestTopla/negatif' runs only that subtest.
Practice Table loop
Write Mutlak(n int) int. Loop over an anonymous struct table of the cases {-3, 3}, {0, 0}, {4, 4}; print how many cases pass.
Starter code
package main
import "fmt"
func main() {
// buraya yaz
}Sample solution
package main
import "fmt"
func Mutlak(n int) int {
if n < 0 {
return -n
}
return n
}
func main() {
tests := []struct{ in, want int }{{-3, 3}, {0, 0}, {4, 4}}
gecen := 0
for _, tt := range tests {
if Mutlak(tt.in) == tt.want {
gecen++
}
}
fmt.Println(gecen)
}Expected output
3
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 What is the advantage of using <code>t.Run</code> in a table test?
- Tests compile faster
- No failure message is needed
- Coverage increases
- Each case is reported as a separate subtest and can be run alone with -run Correct answer
Explanation: Subtest names appear in the output (TestTopla/negatif); even if one case calls Fatal, the others keep running.
2 Subtest
for _, tt := range tests {
t.____(tt.ad, func(t *testing.T) {
// ...
})
}for _, tt := range tests {
t.Run(tt.ad, func(t *testing.T) {
// ...
})
}Explanation: t.Run starts a subtest with the given name.
3 Table part
| Term | Meaning |
|---|---|
ad |
Subtest name |
input fields |
What the function gets |
want |
Expected result |
t.Run |
Separate reporting |