fake function

fake <command> [replacement code] 

Fakes command and replaces it with replacement code (if code is specified) for the rest of the execution of your test. If no replacement code is specified, then it replaces command by one that echoes stdin of fake. This may be useful if you need to simulate an environment for you code under test.

Example

https://github.com/pgrange/bash_unit
For instance examples:

fake ps echo hello world ps 

will output:

hello world 

We can do the same using stdin of fake:

fake ps << EOF hello world EOF ps 

hello world 

It has been asked whether using fake results in creating actual fakes or stubs or mocks? or may be spies? or may be they are dummies? The first answer to this question is: it depends. The second is: read this great and detailed literature on this subject.