Functor tests

tests/test_functors.py

@@ -0,0 +1,24 @@
+import pytest  # type: ignore
+from typing import Callable, Type, TypeVar
+from monads import Functor, Maybe, Result
+
+T = TypeVar("T")
+S = TypeVar("S")
+
+
+@pytest.fixture(scope="module", params=[Maybe, Result])
+def monad(request) -> Type:
+    return request.param
+
+
+def test_identity(monad) -> None:
+    m: Functor = monad.pure(3)
+    identity: Callable[[T], T] = lambda x: x
+    assert m == m.map(identity)
+
+
+def test_associativity(monad) -> None:
+    f: Callable[[int], int] = lambda x: x + 1
+    g: Callable[[int], str] = lambda x: str(x)
+    m: Functor = monad.pure(3)
+    assert m.map(lambda x: g(f(x))) == m.map(f).map(g)