Functions in Powershell - can they be called within a string?
Wrap the command/function call in a subexpression inside an expandable string:
"The results of the test are: $(val "yo!")"
Also worth pointing out, the syntax for command invocation in PowerShell doesn't require parentheses. I would discourage using parentheses like you do in the example altogether, since you'll end up in situations where consecutive arguments are being treated as one:
function val ($inputOne,$inputTwo){ "One: $inputOne" "Two: $inputTwo"}
Now, using C#-like syntax, you'd do:
val("first","second")
but find that the output becomes:
One: first secondTwo:
because the PowerShell parser sees the nested expression ("first","second")
and treats it as a single argument.
The correct syntax for positional parameter arguments would be:
val "first" "second"