Add tests

tests/froude_test.py

@@ -0,0 +1,11 @@
+import pytest
+from scaling import froude
+
+def test_unit_to_same_unit():
+    assert froude.model_to_proto(1, 1, 'm', 'm') == 1
+
+def test_froude_length():
+    assert froude.model_to_proto(1, 10, 'm', 'm') == 10
+
+def test_froude_force():
+    assert froude.model_to_proto(1, 10, 'N', 'N') == 1000