Improve test coverage for broken IC

.coveragerc

@@ -25,3 +25,5 @@ exclude_lines =
     main()
     engine_str == 'gmx'
     if False
+    if self.viz_rotations
+    if self.ForceRebuild:

geometric/tests/test_openmm.py

@@ -55,6 +55,23 @@ def test_dlc_openmm_water3(localizer):
     # Check that the geometry matches the reference to within 0.03 RMS 0.05 max displacement
     assert ((rmsd < 0.03 and maxd < 0.05) or (rmsd2 < 0.03 and maxd2 < 0.05))
 
+@addons.using_openmm
+def test_dlc_openmm_water12(localizer):
+    """
+    Optimize the geometry of twelve water molecules using DLC. 
+    The coordinate system is expected to break down and the optimizer should skip the optimization step
+    after rebuilding the coordinate system.
+    """
+    progress = geometric.optimize.run_optimizer(engine='openmm', pdb=os.path.join(datad,'water12.pdb'), 
+                                                coordsys='dlc', input='tip3p.xml', maxiter=20, converge=['maxiter'])
+
+    have_skip_step = False
+    for line in open('tip3p.log').readlines():
+        if 'Skipping optimization step' in line:
+            have_skip_step = True
+    assert have_skip_step
+
+
 @addons.using_openmm
 def test_tric_openmm_water6(localizer):
     """