Initial Refactoring of yoshi_otter and Test Implementation

tests/algebra/test_algebra.py

@@ -0,0 +1,37 @@
+from yoshi_otter.shared import InvalidFunctionSignature
+from yoshi_otter import algebra as ot
+
+import unittest
+
+
+class TestOtterAlgebra(unittest.TestCase):
+
+    def setUp(self):
+        def f(x):
+            return 2*x
+
+        def g(x, y):
+            return x*y
+
+        self.f = f
+        self.g = g
+
+    def test_class_instantiation(self):
+        algebra = ot.Algebra(self.f)
+        self.assertIsInstance(algebra, ot.Algebra)
+
+    def test_derivative(self):
+        algebra = ot.Algebra(self.f)
+        derivative = algebra.d(0)
+
+        self.assertEqual(derivative, 2)
+
+    def test_derivative_raises_exception(self):
+        algebra = ot.Algebra(self.g)
+
+        with self.assertRaises(InvalidFunctionSignature):
+            algebra.d(0)
+
+
+if __name__ == '__main__':
+    unittest.main()