t.Error and t.Fatal
- Go course
- Intermediate
- Lesson 42/80
- 4 min
Learn t.Error and t.Fatal to report failures.
t.Error and t.Fatal
t.Error / t.Errorf mark the test as failed but keep running, so several failures show up in the same test. t.Fatal / t.Fatalf mark it failed and stop the test immediately.
f, err := os.Open("veri.txt")
if err != nil {
t.Fatalf("açılamadı: %v", err) // no point continuing
}
if got := satirSay(f); got != 3 {
t.Errorf("satır = %d, beklenen 3", got)
}A good failure message
Go convention: what was called, what came back, what was expected — the "got/want" format:
t.Errorf("Parse(%q) = %v, want %v", girdi, got, want)Fatal must not be called inside a goroutine; it only works in the goroutine running the test (because it uses runtime.Goexit). Pass errors from goroutines back to the main test with a channel.
Practice got/want message
Pretend you forgot to implement Buyut(s string) string: it returns s unchanged. For got := Buyut("go") and want := "GO", print the message fmt.Printf("Buyut(%q) = %q, want %q\n", ...).
Starter code
package main
import "fmt"
func main() {
// buraya yaz
}Sample solution
package main
import "fmt"
func Buyut(s string) string { return s }
func main() {
got, want := Buyut("go"), "GO"
if got != want {
fmt.Printf("Buyut(%q) = %q, want %q\n", "go", got, want)
}
}Expected output
Buyut("go") = "go", want "GO"
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 When is t.Fatal preferred?
- When later steps depend on the previous result (e.g. the file failed to open) Correct answer
- Always
- Never
- Only in benchmarks
Explanation: Use Fatal when continuing would cause a nil pointer error or meaningless extra failures; for independent checks Error is enough.
2 Stop the test
if err != nil {
t.____("kurulum başarısız: %v", err)
}if err != nil {
t.Fatalf("kurulum başarısız: %v", err)
}Explanation: Fatalf writes the error and ends the test immediately.
3 Method and behavior
| Term | Meaning |
|---|---|
t.Error |
Fail, continue |
t.Fatal |
Fail, stop |
t.Log |
Just a note |
t.Skip |
Skip the test |