diff --git a/report/report_test.go b/report/report_test.go
index 7979d4a5..d0c20b17 100644
--- a/report/report_test.go
+++ b/report/report_test.go
@@ -37,9 +37,12 @@ func TestTable(t *testing.T) {
 		if got := r.Table(); got != tt.want {
 			t.Errorf("got\n%v\nwant\n%v", got, tt.want)
 		}
-		_ = r.String()
+		orig := r.String()
 		r.Coverage.FlushBlockCoverages()
-		_ = r.String()
+		flushed := r.String()
+		if len(orig) <= len(flushed) {
+			t.Error("FlushBlockCoverages error")
+		}
 	}
 }