Mocker patch at rescue.

Thursday. September 10, 2020 - 1 min

This mini blog would talk about using mocker patch from pytest to mock variables in object creation flow . This patching can be applied to a variable which is used somewhere deep in the codebase with no direct access for mock using conventional techniques. (Conventional techniques meant directly passing an altered/mocked variable).

A scenario:

For creation of app object we use config. This config object is created in the codeflow somewhere inaccessible for direct mocking eg.

• ServiceApp inherits BaseApp
• BaseApp uses Config class to populate self.config variable which is immediately consumed in self.consume_config function in init flow of app.
• Since config sits deep, it’s difficult to inject the mocked value directly at time of app object initialization.

Here comes, mocker.patch to rescue:

1. Create a patch object
   • config_mock = mocker.patch("<complete_path_to_Config_class>")
2. Fetch the method you selectively want to patch
   • get_config_path = config_mock.return_value.get_config
3. Override the return type for this object
   • get_config_path.return_type = <patched_mocked_config_value>
4. Now initialise your app object
   • app = ServiceApp()

The mocked config values would be used instead.

\cheers

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