Examine the 20 slowest tests and make improvements.

[matteius]

On my fast laptop these were the 20 slowest tests:

259.54s call     tests/integration/test_lock.py::test_complex_lock_with_vcs_deps
254.14s call     tests/integration/test_install_uri.py::test_get_vcs_refs
253.65s call     tests/integration/test_install_twists.py::test_multiple_editable_packages_should_not_race
152.11s call     tests/integration/test_install_twists.py::test_local_zipfiles
137.95s call     tests/integration/test_lock.py::test_lock_editable_vcs_with_extras_without_install
133.73s call     tests/integration/test_lock.py::test_lock_nested_direct_url
133.52s call     tests/integration/test_lock.py::test_lock_editable_vcs_without_install
132.87s call     tests/integration/test_install_uri.py::test_install_editable_git_tag
130.86s call     tests/integration/test_lock.py::test_vcs_lock_respects_top_level_pins
130.70s call     tests/integration/test_uninstall.py::test_uninstall_all_local_files
127.40s call     tests/integration/test_install_twists.py::TestDirectDependencies::test_https_dependency_links_install
127.36s call     tests/integration/test_install_uri.py::test_basic_vcs_install_with_env_var
125.63s call     tests/integration/test_install_uri.py::test_basic_vcs_install
125.47s call     tests/integration/test_project.py::test_include_editable_packages
116.35s call     tests/integration/test_install_uri.py::test_editable_vcs_install
113.39s call     tests/integration/test_lock.py::test_lock_editable_vcs_with_markers_without_install
112.68s call     tests/integration/test_uninstall.py::test_uninstall_all_dev
111.80s call     tests/integration/test_lock.py::test_lock_editable_vcs_with_ref_in_git
109.92s call     tests/integration/test_cli.py::test_pipenv_clean_pip_no_warnings
109.60s call     tests/integration/test_install_twists.py::test_relative_paths

Here I examine them, make adjustments to what they should be doing to test (or if they should even exist in a couple cases, due to repeated test cases). After running the tests again: