I made my project with `setuptools` and I want to test it with `tox`. I listed dependencies in a variable and added to `setup()` parameter (`tests_require` and `extras_require`). My project needs to install all of the dependencies listed in `tests_require` to test but `pip install` is not installing them.

I tried this but it did not work:

```
install_command = pip install {opts} {packages}[tests]

```

How can I install test dependencies without having to manage multiple dependency lists (i.e. Having all dependencies listed in both `test_requirements.txt` and the `tests_require` variable)?