Add a test for flexibleConstraints.

wrappers/python/tests/TestForceField.py

@@ -95,6 +95,29 @@ class TestForceField(unittest.TestCase):
                 validateConstraints(self, topology, system,
                                     constraints_value, rigidWater_value)
 
+    def test_flexibleConstraints(self):
+        """ Test the flexibleConstraints keyword """
+        topology = self.pdb1.topology
+        system1 = self.forcefield1.createSystem(topology, constraints=HAngles,
+                                                rigidWater=True)
+        system2 = self.forcefield1.createSystem(topology, constraints=HAngles,
+                                                rigidWater=True, flexibleConstraints=True)
+        validateConstraints(self, topology, system1, HAngles, True)
+        validateConstraints(self, topology, system2, HAngles, True)
+        for force in system1.getForces():
+            if isinstance(force, HarmonicBondForce):
+                bf1 = force
+            elif isinstance(force, HarmonicAngleForce):
+                af1 = force
+        for force in system2.getForces():
+            if isinstance(force, HarmonicBondForce):
+                bf2 = force
+            elif isinstance(force, HarmonicAngleForce):
+                af2 = force
+        # Make sure we picked up extra terms with flexibleConstraints
+        self.assertGreater(bf2.getNumBonds(), bf1.getNumBonds())
+        self.assertGreater(af2.getNumAngles(), af2.getNumAngles())
+
     def test_ImplicitSolvent(self):
         """Test the four types of implicit solvents using the implicitSolvent
         parameter.