Fix/mech5003 (#245)

* Added tests for MECH5003 issue

* Added pre-processing of the reserved keyword 'as'

* Fixed preview tests

* Fixed tests

* Updated test names

Author: m-messer

app/evaluation_tests.py

@@ -215,6 +215,30 @@ def test_mu_preview_evaluate(self):
         result = evaluation_function(response, answer, params)
         assert result["is_correct"] is True
 
+    @pytest.mark.parametrize(
+        "response, is_latex, is_correct", [
+            ("A/s(e**(-a*s)-e**(-b*s))", False, True),
+            ("A/s(e**(-as)-e**(-bs))", False, True),
+            ("(A/s)( e^{-a*s}-e^{-b*s})", True, True),
+            ("(A/s)( e^{-as}-e^{-bs})", True, True),
+            (r"\frac{A}{s} (e^{-a*s}-e^{-b*s})", True, True),
+            (r"\frac{A}{s} (e^{-a s}-e^{-b s})", True, True)
+        ]
+    )
+    def test_laplace_transforms(self, response, is_latex, is_correct):
+
+        params = {
+            "is_latex": is_latex,
+            "strict_syntax": False,
+            "elementary_functions": True,
+            "convention": "implicit_higher_precedence",
+        }
+        answer = "A/s(e**(-a*s)-e**(-b*s))"
+
+        result = evaluation_function(response, answer, params)
+        assert result["is_correct"] == is_correct
+
+
 
 if __name__ == "__main__":
     pytest.main(['-xk not slow', '--tb=short', '--durations=10', os.path.abspath(__file__)])

app/preview_tests.py

@@ -227,6 +227,27 @@ def test_multi_character_implicit_multi_variable(self):
         assert result["preview"]["latex"] =='\\frac{a}{bc \\cdot d}'
         assert result["preview"]["sympy"] == "a/bcd"
 
+    @pytest.mark.parametrize(
+        "response, is_latex, latex, sympy", [
+            ("A/s(e**(-a*s)-e**(-b*s))", False, r"\frac{A \cdot \left(e^{- a \cdot s} - e^{- b \cdot s}\right)}{s}", "A/s( E**(-a*s)- E**(-b*s))"),
+            ("A/s(e**(-as)-e**(-bs))", False, r"\frac{A \cdot \left(e^{- a \cdot s} - e^{- b \cdot s}\right)}{s}", "A/s( E**(-a*s)- E**(-bs))"),
+            ("(A/s)( e^{-a*s}-e^{-b*s})", True, r"(A/s)( e^{-a*s}-e^{-b*s})", "A*(-exp(-b*s) + exp(-a*s))/s"),
+            ("(A/s)( e^{-as}-e^{-bs})", True, r"(A/s)( e^{-as}-e^{-bs})", "A*(-exp(-b*s) + exp(-a*s))/s"),
+        ]
+    )
+    def test_laplace_transforms(self, response, is_latex, latex, sympy):
+        params = {
+            "is_latex": is_latex,
+            "strict_syntax": False,
+            "elementary_functions": True,
+            "convention": "implicit_higher_precedence",
+        }
+
+        result = preview_function(response, params)
+        assert result["preview"]["latex"] == latex
+        assert result["preview"]["sympy"] == sympy
+
+
 
 if __name__ == "__main__":
     pytest.main(['-xk not slow', "--tb=line", os.path.abspath(__file__)])

app/utility/expression_utilities.py

@@ -412,6 +412,10 @@ def substitute_input_symbols(exprs, params):
     # we need to make sure it is not substituted back in
     substitutions = [(original, subs.replace("lambda", "lamda")) for (original, subs) in substitutions]
 
+    # Since 'as' is a reserved keyword in python, we add a subsitution of 'as' to 'a*s' if 'as' is not a defined symbol
+    if 'as' not in input_symbols.keys():
+        substitutions += [('as', 'a*s')]
+
     substitutions = list(set(substitutions))
     if len(substitutions) > 0:
         substitutions.sort(key=substitutions_sort_key)