cmd/testwrapper/flakytest: clearly describe why TestFlakeRun fails

Fixes tailscale#8474

Signed-off-by: Maisem Ali <[email protected]>

Author: Maisem Ali

cmd/testwrapper/flakytest/flakytest_test.go

@@ -28,13 +28,16 @@ func TestIssueFormat(t *testing.T) {
 	}
 }
 
+// TestFlakeRun is a test that fails when run in the testwrapper
+// for the first time, but succeeds on the second run.
+// It's used to test whether the testwrapper retries flaky tests.
 func TestFlakeRun(t *testing.T) {
 	Mark(t, "https://github.com/tailscale/tailscale/issues/0") // random issue
 	e := os.Getenv(FlakeAttemptEnv)
 	if e == "" {
 		t.Skip("not running in testwrapper")
 	}
 	if e == "1" {
-		t.Fatal("failing on purpose")
+		t.Fatal("First run in testwrapper, failing so that test is retried. This is expected.")
 	}
 }