[mschuster91]

Often enough software has dependencies on external services (think of stuff like a CRM database, payment and shipping providers, integrations with CDNs, external identity verification services) where one has to go with mocks for testing if stuff like error handling etc. works.

[alquemist]

Fake external storage / rpc dependencies.

[vbezhenar]

That's called mocking...

[alquemist]

Mock: Adhoc guessing of what methods called on a dependency, but sometimes even between classes in the same module, might return. Guess repeated over and over as new tests are added, sometimes tens of times or even more. For example, https://site.mockito.org/#how, "when(mockedList.get(0)).thenReturn("first"); System.out.println(mockedList.get(0)); // prints "first""

Fake: A replacement module that behaves like a production module, but with certain simplifications, for example in-process vs. using rpcs, or simply cleaning up the filesystem after usage. For example, https://github.com/tk0miya/testing.postgresql. "automatically setups a postgresql instance in a temporary directory, and destroys it after testing".