Merge branch 'Issue-740' into 'master'

Handle load of Service with missing Plugin - Issue 740

Closes #740

See merge request openlp/openlp!288

openlp/core/state.py

@@ -147,11 +147,15 @@ class State(LogMixin, metaclass=Singleton):
         :return: Have the preconditions been met.
         :rtype: bool
         """
+        try:
             if self.modules[name].requires is None:
                 return self.modules[name].pass_preconditions
             else:
                 mod = self.modules[name].requires
                 return self.modules[mod].pass_preconditions
+        except KeyError:
+            # Module is missing so therefore not found.
+            return False
 
     def list_plugins(self):
         """

tests/functional/openlp_core/test_state.py

@@ -207,3 +207,20 @@ def test_check_preconditions_required_module(state):
 
     # THEN: The correct result should be returned
     assert result is False
+
+
+def test_check_preconditions_missing_module(state):
+    """
+    Test that the check_preconditions() method returns the correct attribute when the module is missing
+    """
+    # GIVEN: A State with two modules
+    State().modules.update({
+        'test_pre2': MagicMock(requires='test_pre3', pass_preconditions=True),
+        'test_pre3': MagicMock(requires=None, pass_preconditions=False)
+    })
+
+    # WHEN: check_preconditions() is called
+    result = State().check_preconditions('test_pre1')
+
+    # THEN: The correct result should be returned
+    assert result is False