More mypy (#612)

* remove type comment where type is annotated
* move function tests
* remove six from tests
* add none annotations
* add more types
* change mock (so that mypy understands it)

test/test_functions/test_functions.py

@@ -0,0 +1,27 @@
+import pytest
+
+from escpos.printer import Dummy
+
+
+def test_line_spacing_code_gen() -> None:
+    printer = Dummy()
+    printer.line_spacing(10)
+    assert printer.output == b"\x1b3\n"
+
+
+def test_line_spacing_rest() -> None:
+    printer = Dummy()
+    printer.line_spacing()
+    assert printer.output == b"\x1b2"
+
+
+def test_line_spacing_error_handling() -> None:
+    printer = Dummy()
+    with pytest.raises(ValueError):
+        printer.line_spacing(99, divisor=44)
+    with pytest.raises(ValueError):
+        printer.line_spacing(divisor=80, spacing=86)
+    with pytest.raises(ValueError):
+        printer.line_spacing(divisor=360, spacing=256)
+    with pytest.raises(ValueError):
+        printer.line_spacing(divisor=180, spacing=256)