Add test for dimension in cos()

tests/test_equations.py

@@ -11,7 +11,7 @@
                                   derive_baseunit)
 from essm.variables.utils import (extract_variables, replace_defaults,
                                   replace_variables)
-from sympy import Derivative, exp, log, S, Symbol, solve, sqrt
+from sympy import cos, Derivative, exp, log, S, Symbol, solve, sqrt
 from sympy.physics.units import Quantity, length, meter
 
 
@@ -114,12 +114,19 @@ class valid_units(Equation):
 
 
 def test_units_exp():
-    """Check units in exp. SHOULD FAIL!"""
+    """Check units in exp."""
 
     class valid_units_exp(Equation):
         expr = Eq(demo_d/demo_d1, exp(demo_1))
 
 
+def test_units_cos():
+    """Check units in cos."""
+
+    class valid_units_exp(Equation):
+        expr = Eq(1, 1/(cos(demo_1)))
+
+
 def test_integrate():
     """Test that variables can be used as integration symbols."""
     from sympy import integrate