Overview and example of mocking an AES encryption library

cmac_aes_mock.c

// Bird's-eye view of overall production code
Cmac_Calculate()
{
    aes_handle = Aes128_Create(key, iv)
    
    // Perform several technical operations (CmacOps) per the CMAC spec.
    CmacOps_GenerateSubkeys(aes_handle, *subkey1, *subkey2)
    //...
    CmacOps_ApplyCbcMac(aes_handle, <relevant_parameters>)
    //...
}

// The individual steps are internally complex - test each.

// Test an individual operation; high level view
TEST(generate_subkeys)
{
    // Setup
    aes_handle = Aes128_Create(key, iv)

    // Test
    CmacOps_GenerateSubkeys(aes_handle, *subkey1, *subkey2)
    
    // Verify
    CHECK(expected, subkey1)
    CHECK(expected, subkey2)
    
    // Teardown
    Aes128_Destroy(aes_handle)
}