tests: adds explicit dictionary type cost call

tests/unit/test_cost.py

@@ -29,10 +29,12 @@ def ground_truth(self):
 
     @pytest.fixture
     def parameters(self):
-        return pybop.Parameter(
-            "Negative electrode active material volume fraction",
-            prior=pybop.Gaussian(0.5, 0.01),
-            bounds=[0.375, 0.625],
+        return pybop.Parameters(
+            pybop.Parameter(
+                "Negative electrode active material volume fraction",
+                prior=pybop.Gaussian(0.5, 0.01),
+                bounds=[0.375, 0.625],
+            )
         )
 
     @pytest.fixture
@@ -116,7 +118,8 @@ def test_base(self, model, parameters, dataset):
             with pytest.raises(NotImplementedError):
                 base_cost([0.5])
 
-    def test_costs(self, cost):
+    def test_costs(self, cost, parameters):
+        # Test cost direction
         if isinstance(cost, pybop.BaseLikelihood):
             higher_cost = cost([0.52])
             lower_cost = cost([0.55])
@@ -129,6 +132,7 @@ def test_costs(self, cost):
 
         # Test type of returned value
         assert np.isscalar(cost([0.5]))
+        assert np.isscalar(cost(parameters.as_dict()))
 
         # Test UserWarnings
         if isinstance(cost, (pybop.SumSquaredError, pybop.RootMeanSquaredError)):