Turns out I'm a massive idiot and I was just running the tests with the wrong keyboard shortcut - doh! Here are the shortcuts I was using and the ones I am now using:
Ctrl r + Ctrl t => Run tests in current context (debug mode)- Ctrl r + t => Run tests in current context
Ctrl r + Ctrl a => Run all tests in solution (debug mode)- Ctrl r + a => Run all tests in solution