Some update modifiers only have c++ unit tests but no jstests.

In particular there are none for:

• $mul
• $bit
• $min
• $max
• $currentDate

While these test are not strictly needed it is helpful to provide runnable tests which are easy for everyone to understand without reading C++, or the unit test framework. These tests need not be exhaustive nor repeat what already exists but they should cover the common use cases more as example of syntax and best practices.