Add static interface implementation check

Add an additional line of code per interface to the generated mock file,
which allows the go compiler to statically check if the mock implements
the mocked interface.

generate/generated.go

@@ -13,6 +13,10 @@ var (
 	lockMyInterfaceMockTwo   sync.RWMutex
 )
 
+// Ensure, that MyInterfaceMock does implement MyInterface.
+// If this is not the case, regenerate this file with moq.
+var _ MyInterface = &MyInterfaceMock{}
+
 // MyInterfaceMock is a mock implementation of MyInterface.
 //
 //     func TestSomethingThatUsesMyInterface(t *testing.T) {