Add test for seq delay

Author: dbrattli

.pre-commit-config.yaml

@@ -1,31 +1,30 @@
 exclude: "_version.py|versioneer.py"
 repos:
-- hooks:
-    - args:
-        - --remove-all-unused-imports
-        - --in-place
-      id: autoflake
-  repo: https://github.com/humitos/mirrors-autoflake
-  rev: v1.1
-- hooks:
-    - id: isort
-  repo: https://github.com/timothycrosley/isort
-  rev: 5.6.4
-- hooks:
-    - id: black
-  repo: https://github.com/psf/black
-  rev: 20.8b1
-- hooks:
-    - id: flake8
-  repo: https://gitlab.com/pycqa/flake8
-  rev: 3.8.4
-- hooks:
-  - id: pyright
-    name: pyright
-    entry: pyright
-    language: node
-    pass_filenames: false
-    types: [python]
-    additional_dependencies: ['[email protected]']
-  repo: local
-  
+  - hooks:
+      - args:
+          - --remove-all-unused-imports
+          - --in-place
+        id: autoflake
+    repo: https://github.com/humitos/mirrors-autoflake
+    rev: v1.1
+  - hooks:
+      - id: isort
+    repo: https://github.com/timothycrosley/isort
+    rev: 5.6.4
+  - hooks:
+      - id: black
+    repo: https://github.com/psf/black
+    rev: 20.8b1
+  - hooks:
+      - id: flake8
+    repo: https://gitlab.com/pycqa/flake8
+    rev: 3.8.4
+  - hooks:
+      - id: pyright
+        name: pyright
+        entry: pyright
+        language: node
+        pass_filenames: false
+        types: [python]
+        additional_dependencies: ["[email protected]"]
+    repo: local

tests/test_seq.py

@@ -212,6 +212,22 @@ def test_seq_pipeline(xs: List[int]):
     assert ys == functools.reduce(lambda s, x: s + x, filter(lambda x: x > 100, map(lambda x: x * 10, xs)), 0)
 
 
+@given(st.lists(st.integers()))
+def test_seq_delay(xs: List[int]):
+    ran = False
+
+    def generator():
+        nonlocal ran
+        ran = True
+        return seq.of_list(xs)
+
+    ys = seq.delay(generator)
+    assert not ran
+
+    assert list(ys) == xs
+    assert ran
+
+
 def test_seq_choose_option():
     xs: Iterable[Optional[int]] = seq.of(None, 42)