Add unit tests for Either monad

test/types/test_Either.py

@@ -0,0 +1,135 @@
+from pytest import raises, fixture
+
+from modules.types.Either import Either, Left, Right
+
+def test_is_right():
+	assert not Left(12).is_right
+	assert Right("str").is_right
+
+def test_val():
+	assert Right("str").val == "str"
+	with raises(TypeError):
+		Left(12).val
+
+def test_lval():
+	assert Left(12).lval == 12
+	with raises(TypeError):
+		Right("str").lval
+
+def test_equals():
+	assert Left(12) == Left(12)
+	assert Left(12) != Left(13)
+	assert Left(12) != Left("12")
+
+	assert Right(12) == Right(12)
+	assert Right(12) != Right(13)
+	assert Right(12) != Right("12")
+
+	assert Right(12) != Left(12)
+
+def test_map_right():
+	transform = lambda x: f"my {x}"
+
+	assert Right("str").map(transform) == Right("my str")
+	assert Right(12).map(transform)    == Right("my 12")
+
+def test_map_left():
+	transform = lambda x: f"my {x}"
+
+	assert Left("str").map(transform) == Left("str")
+	assert Left(12).map(transform)    == Left(12)
+
+def test_compound_map_right():
+	tf_a = lambda x: f"precious {x}"
+	tf_b = lambda x: f"my {x}"
+
+	assert Right("str").map(tf_a).map(tf_b) == Right("my precious str")
+	assert Right(12).map(tf_a).map(tf_b)    == Right("my precious 12")
+
+def test_compound_map_left():
+	tf_a = lambda x: f"precious {x}"
+	tf_b = lambda x: f"my {x}"
+
+	assert Left("str").map(tf_a).map(tf_b) == Left("str")
+	assert Left(12).map(tf_a).map(tf_b)    == Left(12)
+
+def test_flat_map_right_to_right():
+	transform = lambda x: Right(f"my {x}")
+
+	assert Right("str").flat_map(transform) == Right("my str")
+	assert Right(12).flat_map(transform)    == Right("my 12")
+
+def test_flat_map_right_to_left():
+	transform = lambda x: Left(f"my {x}")
+
+	assert Right("str").flat_map(transform) == Left("my str")
+	assert Right(12).flat_map(transform)    == Left("my 12")
+
+def test_flat_map_left_to_left():
+	transform = lambda x: Left(f"my {x}")
+
+	assert Left("str").flat_map(transform) == Left("str")
+	assert Left(12).flat_map(transform)    == Left(12)
+
+def test_flat_map_left_to_right():
+	transform = lambda x: Right(f"my {x}")
+
+	assert Left("str").flat_map(transform) == Left("str")
+	assert Left(12).flat_map(transform)    == Left(12)
+
+def test_flat_map_long_chain():
+	assert Right("str").flat_map(
+		lambda x: Right(f"precious {x}")
+	).flat_map(
+		lambda x: Right(f"my {x}")
+	).flat_map(
+		lambda x: Right(f"wow, {x}")
+	) == Right("wow, my precious str")
+
+def test_flat_map_and_map_chain():
+	def fn_stoi(x: str) -> Either[Exception, int]:
+		try:
+			return Right(int(x))
+		except Exception as e:
+			return Left(e)
+
+	def fn_do_invert(x: int) -> Either[Exception, float]:
+		try:
+			return Right(1/x)
+		except Exception as e:
+			return Left(e)
+
+	def fn_do_stringify(x: float) -> str:
+		return f"wow, it's {x:.4}!"
+
+	res = Right("12") \
+		.flat_map(fn_stoi) \
+		.flat_map(fn_do_invert) \
+		.map(fn_do_stringify)
+
+	print(f"Computation result: {res}")
+	assert res == Right("wow, it's 0.08333!")
+
+def test_cancelled_chain():
+	def fn_stoi(x: str) -> Either[Exception, int]:
+		try:
+			return Right(int(x))
+		except Exception as e:
+			return Left(e)
+
+	def fn_do_invert(x: int) -> Either[Exception, float]:
+		try:
+			return Right(1/x)
+		except Exception as e:
+			return Left(e)
+
+	def fn_do_stringify(x: float) -> str:
+		return f"wow, it's {x:.4}!"
+
+	res = Right("0") \
+		.flat_map(fn_stoi) \
+		.flat_map(fn_do_invert) \
+		.map(fn_do_stringify)
+
+	assert not res.is_right
+	assert res.lval.__class__.__name__ == 'ZeroDivisionError'