Related issues

Is your feature request related to a problem? Please describe.
Until this extension can run 'subtest at cursor' reliably (#1602), an easier and more flexible way to allow people to run arbitrary subtests is to add a "Test -run" command that allows people to run tests with a custom value for -run flag. I think this command will still remain useful even when 'subtest at cursor' command can run reliably because you can write regexp to match and run multiple subtests at any level, not just one specific subtest under your cursor.

Describe the solution you'd like
Add a command that works like "Test Package" except it should show an input box that allows specifying a custom value for -run flag before running tests. Subsequent runs of this command should remember the previous value to make typing minimal.