diff --git a/pkg/capture/capture_test.go b/pkg/capture/capture_test.go
new file mode 100644
index 000000000..af3a01175
--- /dev/null
+++ b/pkg/capture/capture_test.go
@@ -0,0 +1,22 @@
+package capture
+
+import (
+	"fmt"
+	"os"
+	"testing"
+)
+
+func TestOutputMergesStdoutAndStderr(t *testing.T) {
+	got := Output(func() {
+		fmt.Print("out")
+		fmt.Fprint(stderrWriter(), "err") // write directly to stderr
+	})
+	if got != "outerr" {
+		t.Fatalf("unexpected combined output: %q", got)
+	}
+}
+
+// stderrWriter returns the current process stderr; split for test clarity.
+func stderrWriter() *os.File {
+	return os.Stderr
+}