core tests - print unprocessed calls in pytest verbose mode

e.g. if you start test with pytest test_style.py -vv it will be easier to guess why it couldn't find a call
```
E               Exception: <class 'abc.Ifc'> was not called with run:
E                - {'type': 'SHOULD_BE_CALLED', 'number': None, 'call': {'name': 'run', 'args': ('style.add_surface_style',), 'kwargs': {'style': 'style', 'ifc_class': 'IfcSurfaceStyleShading', 'attributes': 'attributes'}}}
E               Unprocessed calls:
E                - {'name': 'run', 'args': ('style.add_style',), 'kwargs': {'name': 'name'}}
E                - {'name': 'link', 'args': ('element', 'obj'), 'kwargs': {}}
E                - {'name': 'run', 'args': ('style.add_surface_style',), 'kwargs': {'style': 'element', 'ifc_class': 'IfcSurfaceStyleShading', 'attributes': 'attributes'}}
```

src/blenderbim/test/core/bootstrap.py

@@ -16,6 +16,7 @@
 # You should have received a copy of the GNU General Public License
 # along with BlenderBIM Add-on.  If not, see <http://www.gnu.org/licenses/>.
 
+import sys
 import json
 import pytest
 import blenderbim.core.tool
@@ -293,4 +294,15 @@ class Prophecy:
                 raise Exception(f"Called {count}: {prediction}")
         else:
             if prediction["call"] not in self.calls:
-                raise Exception(f"{self.subject} was not called with {prediction['call']['name']}: {prediction}")
+                error_msg = f"{self.subject} was not called with {prediction['call']['name']}:\n - {prediction}"
+
+                # Print all unprocessed calls if pytest was started in verbose mode.
+                if "-v" in sys.argv or "-vv" in sys.argv:
+                    if not self.calls:
+                        error_msg += "\nNo unprocessed calls."
+                    else:
+                        error_msg += "\nUnprocessed calls:"
+                        for call in self.calls:
+                            error_msg += f"\n - {call}"
+
+                raise Exception(error_msg)