Add more tests for Maybe

tests/test_maybe.py

@@ -1,21 +1,68 @@
 import pytest  # type: ignore
-from typing import List
+from typing import Callable, List
+
 from monads.maybe import Maybe, Just, Nothing, maybe, first, last
 
 
-def test_maybe_none():
+def test_bind_just() -> None:
+    m: Maybe[int] = Just(5)
+    increment: Callable[[int], Maybe[int]] = lambda x: Just(x + 1)
+    assert Just(6) == m.bind(increment)
+
+
+def test_bind_nothing() -> None:
+    m: Maybe[int] = Nothing()
+    increment: Callable[[int], Maybe[int]] = lambda x: Just(x + 1)
+    assert Nothing() == m.bind(increment)
+
+
+def test_apply_just_to_just() -> None:
+    m: Maybe[int] = Just(5)
+    increment: Callable[[int], int] = lambda x: x + 1
+    assert Just(6) == m.apply(Maybe.pure(increment))
+
+
+def test_apply_just_to_nothing() -> None:
+    m: Maybe[int] = Nothing()
+    increment: Callable[[int], int] = lambda x: x + 1
+    assert Nothing() == m.apply(Maybe.pure(increment))
+
+
+def test_apply_nothing_to_just() -> None:
+    m: Maybe[int] = Just(5)
+    f: Maybe[Callable[[int], int]] = Nothing()
+    assert Nothing() == m.apply(f)
+
+
+def test_apply_nothing_to_nothing() -> None:
+    m: Maybe[int] = Nothing()
+    f: Maybe[Callable[[int], int]] = Nothing()
+    assert Nothing() == m.apply(f)
+
+
+def test_just_withdefault() -> None:
+    m: Maybe[int] = Just(5)
+    assert 5 == m.withDefault(0)
+
+
+def test_nothing_withdefault() -> None:
+    m: Maybe[int] = Nothing()
+    assert 0 == m.withDefault(0)
+
+
+def test_maybe_none() -> None:
     assert isinstance(maybe(None), Nothing)
 
 
-def test_maybe_something():
+def test_maybe_something() -> None:
     assert isinstance(maybe(False), Just)
 
 
-def test_maybe_boolean_false():
+def test_maybe_boolean_false() -> None:
     assert isinstance(maybe(False, predicate=bool), Nothing)
 
 
-def test_maybe_boolean_true():
+def test_maybe_boolean_true() -> None:
     assert isinstance(maybe(True, predicate=bool), Just)
 
 
@@ -23,6 +70,7 @@ def test_first() -> None:
     maybes: List[Maybe[int]] = [Nothing(), Just(1), Just(2)]
     assert Just(1) == first(maybes)
 
+
 def test_last() -> None:
     maybes: List[Maybe[int]] = [Just(1), Just(2), Nothing()]
     assert Just(2) == last(maybes)