Test coverage has nothing to do with module installation. However, build systems are for both those who install modules and those who create modules. Otherwise, it might make more sense to call this Module::Install or Module::Create. Since you can't have the former without the latter, why create a build system that only caters to one segment? I am not suggesting that this be one of the first features put in there, but it would be a valuable one.
Test coverage is an important (but neglected) part of ensuring software quality. Any tool that makes it easier to provide better quality software can only help Perl.