[thin_delta] Print usage on unrecognised switch

features/thin_delta.feature

@@ -27,3 +27,7 @@ Feature: thin_delta
       {-h|--help}
       {-V|--version}
     """
+
+  Scenario: Unrecognised option should cause failure
+    When I run `thin_delta --unleash-the-hedeghogs`
+    Then it should fail

thin-provisioning/thin_delta.cc

@@ -37,6 +37,10 @@ int main(int argc, char **argv)
 		case 'V':
 			cout << THIN_PROVISIONING_TOOLS_VERSION << endl;
 			return 0;
+
+		default:
+			usage(cerr, basename(argv[0]));
+			return 1;
 		}
 	}