diff --git a/__test__/satysrc/generic.saty b/__test__/satysrc/generic.saty
index 3b2fdff..38da84d 100644
--- a/__test__/satysrc/generic.saty
+++ b/__test__/satysrc/generic.saty
@@ -37,16 +37,6 @@
 @import: ../../src/tree-map
 @import: ../../src/big-int
 
-let () = Debug.log `==== Promise ====` in
-let p = Promise.delay ~(!!(&(let () = Debug.log `foo` in 1))) in
-let () = Debug.log `bar` in
-let _ = Promise.force p in
-let _ = Promise.force p in
-let p = Promise.delay ~(!!(&(let () = Debug.log `foobar` in 3.14))) in
-let () = Debug.log `barbaz` in
-let _ = Promise.force p in
-let _ = Promise.force p in
-
 let () = Debug.log `==== Float ====` in
 let p f = f |> String.of-float |> Debug.log in
 let () = p Float.pi in
diff --git a/test/main.test.saty b/test/main.test.saty
index af679dc..5ce72e1 100644
--- a/test/main.test.saty
+++ b/test/main.test.saty
@@ -13,6 +13,7 @@
 @import: list.test
 @import: map.test
 @import: parser.test
+@import: promise.test
 @import: ref.test
 @import: regex.test
 @import: string.test
@@ -26,6 +27,7 @@ describe `base` [
   list-test-cases;
   map-test-cases;
   parser-test-cases;
+  promise-test-cases;
   ref-test-cases;
   regex-test-cases;
   string-test-cases;
diff --git a/test/promise.test.satyg b/test/promise.test.satyg
new file mode 100644
index 0000000..7b0a12f
--- /dev/null
+++ b/test/promise.test.satyg
@@ -0,0 +1,20 @@
+@require: test/test
+@require: test/expect
+
+@import: ../src/base0
+@import: ../src/ref
+@import: ../src/promise
+
+let promise-test-cases = open Test in
+  describe `Promise module` [
+    it `evaluate lazily` (fun () -> (
+      let r = Ref.make 0 in
+      let p = Promise.delay ~(!!(&(let () = r |> Ref.inc in 1))) in
+      Ref.get r == 0
+      && (let _ = Promise.force p in
+      Ref.get r == 1
+      && (let _ = Promise.force p in
+      Ref.get r == 1))
+      |> Expect.is-true
+    ));
+  ]