Description

The tests in observer_test.cpp that call helper function testGetDataReceivedPerSecondByFillingBuffer are flaky in CI because they rely on the passage of actual time.

This PR adds a FakeClock that simulates the passage of time and can be substituted for any std::chrono clock. The time point of FakeClock is fixed and can be explicitly advanced forward with FakeClock::advance. Observer now has a template arg that specifies the clock to use (default is std::chrono::steady_clock) which enables usage of FakeClock in observer_test.cpp.

Testing Done

• observer_test.cpp passes
• Added fake_clock_test.cpp

Resolved Issues

Resolves #3309

Length Justification and Key Files to Review

Review Checklist

It is the reviewers responsibility to also make sure every item here has been covered

• Function & Class comments: All function definitions (usually in the .h file) should have a javadoc style comment at the start of them. For examples, see the functions defined in thunderbots/software/geom. Similarly, all classes should have an associated Javadoc comment explaining the purpose of the class.
• Remove all commented out code
• Remove extra print statements: for example, those just used for testing
• Resolve all TODO's: All TODO (or similar) statements should either be completed or associated with a github issue