Added test.

wrappers/python/tests/TestAmberPrmtopFile.py

@@ -275,5 +275,25 @@ class TestAmberPrmtopFile(unittest.TestCase):
                 diff = norm(f1-f2)
                 self.assertTrue(diff < 0.1 or diff/norm(f1) < 1e-4)
 
+    def test_with_dcd_reporter(self):
+        """Check that an amber simulation like the docs example works with a DCD reporter."""
+
+        temperature = 50*kelvin
+
+        prmtop = prmtop4  # Mg + water
+        inpcrd = inpcrd4  # Mg + water
+        system = prmtop.createSystem(nonbondedMethod=PME, nonbondedCutoff=1*nanometer, constraints=HBonds)
+        system.addForce(MonteCarloBarostat(1.0 * atmospheres, temperature, 1))
+
+        integrator = LangevinIntegrator(temperature, 1.0 / picosecond, 0.0001 * picoseconds)
+        
+        simulation = Simulation(prmtop.topology, system, integrator)
+        simulation.context.setPositions(inpcrd.positions)
+        simulation.context.setPeriodicBoxVectors(*inpcrd.boxVectors)
+
+        simulation.reporters.append(DCDReporter('output.dcd', 1))  # This is an explicit test for the bugs in issue #850
+        simulation.step(5)
+        
+
 if __name__ == '__main__':
     unittest.main()