A lot of developers I have worked with have been amazed to see that I expand a suite of tests they developed by a factor of four. This is almost always because I am stressing error handling which is often not tested at all. Unfortunately, these tests will often cause many warnings. Sometimes I want to verify the exact warning. Other times it just clutters the output being sent to the screen. This can be very dangerous – it may lead someone running the test to believe there is a newly introduced bug.

Luckily, perl has a well defined mechanism for overriding the warn behavior. If you want to suppress warnings from being displayed in a section of tests do the following:

    • Scope the section of code where you want to suppress the warnings:
      { ... }
      Define your own warning handler inside the scoped code:

           local $SIG{__WARN__}=sub{}; #Temporarily suppress warnings

           # Insert test code here

  • Once the scoping ends, whatever warning handler was in effect before will be active again.