Many of the PowerShell commands are made out of functions. Here is how you can peek into the source code of any function:
(Get-Command Test-NetConnection).Definition
Just make sure the command you want to examine does exist, and is a function. Test-NetConnection is available on Windows 8/Server 2012 or better. To see a list of all functions available for spying, use this:
PS> Get-Command -CommandType Function
