test: add a panic catcher test

internal/catch/catch.go

@@ -2,13 +2,16 @@ package catch
 
 import (
 	"fmt"
+	"io"
 	"os"
 	"runtime/debug"
 )
 
+var panicWriter io.Writer = os.Stderr
+
 func CatchAndLog(err *error, where string) {
 	if rerr := recover(); rerr != nil {
-		fmt.Fprintf(os.Stderr, "caught panic: %s\n%s\n", rerr, debug.Stack())
+		fmt.Fprintf(panicWriter, "caught panic: %s\n%s\n", rerr, debug.Stack())
 		*err = fmt.Errorf("panic in %s: %s", where, rerr)
 	}
 }

internal/catch/catch_test.go

@@ -0,0 +1,28 @@
+package catch
+
+import (
+	"bytes"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestCatch(t *testing.T) {
+	buf := new(bytes.Buffer)
+
+	oldPanicWriter := panicWriter
+	t.Cleanup(func() { panicWriter = oldPanicWriter })
+	panicWriter = buf
+
+	panicAndCatch := func() (err error) {
+		defer CatchAndLog(&err, "somewhere")
+
+		panic("here")
+	}
+
+	err := panicAndCatch()
+	require.Error(t, err)
+	require.Contains(t, err.Error(), "panic in somewhere: here")
+
+	require.Contains(t, buf.String(), "caught panic: here")
+}