diff --git a/tests/STRING_test.ts b/tests/STRING_test.ts
index 0be3b19..e3aa435 100644
--- a/tests/STRING_test.ts
+++ b/tests/STRING_test.ts
@@ -90,4 +90,11 @@ Deno.test("STRING adapt test", () => {
   Deno.test("STRING adapt via do() test", () => {
     const t = STRING("hello").contains("hello").do((prev: string)=>prev += " world").getValue();
     assertStringIncludes(t, "hello world");
+  });
+
+  Deno.test("STRING does not change if do method is not reached", () => {
+    const t = STRING("hello")
+    .contains("x")
+    .do((prev: string)=>prev += " world").getValue();
+    assertStringIncludes(t, "hello");
   });
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