Ceedling: mock hardware software interface by using StubWithCallback

     Auto generated mock files in Ceedling provides Ignore and Expect functions as well as StubWithCallback function. StubWithCallback demonstrates hardware software interface. For example, external EEPROM can be accessed via specific SPI command such as read byte and write byte. It means that there is no direct way to access EEPROM contents. It would be nice to access EEPROM during unit testing. To do this, define simulated EEPROM in host RAM and the read byte function and write byte function should be implemented as StubWIthCallback. I learned this Ceedling feature from this blog(http://www.electronvector.com/blog/unit-testing-with-flash-eeprom). 

    First of all, create interface_flash.h:

    Second, create eeprom_controller module, ceedling module:create[eeprom_controller].

eeprom_read_byte calls flash_read function and eeprom_write_byte calls flash_write function and EEPROM size is defined 8KB. These wrapper functions will be implemented next post.

    Third, flash_read and flash_write function should be known as mock function so that it needs to include "mock_interface_flash.h" in line#4 below. Then, implement mock_read function and mock_write function in test_eeprom_controller.c. mock_read function is replacing flash_read during unit testing. mock_write function is replacing flash_write during unit testing. This replacement during unit testing is done by StubWithCallback in Ceedling. Implementation is in test file line#37, 38 below. Also, Simulated EEPROM in host needs to be defined in test file line#6 below.

    Fourth, write a test for SutbWithCallback. This test is necessary to prove mock functions are working as expected. line#49 should update mock_eeprom[0] = 0xAA. line#52 should set read_data = mock_eeprom[0]. line#53 assertion for mock_eeprom[0] = 0xAA.

    Next post will show Test Driven Development process while implementing eeprom_read_byte function and eeprom_write_byte function in eeprom_controller.c. It will evolve with test_eeprom_controller.c.