Add test-requirements.txt for pip install

Adapted the circleci config to implement the changes made by #200 and #201

Author: nor3th

.circleci/config.yml

@@ -11,6 +11,9 @@ jobs:
       - run:
           name: install dependencies
           command: pip3 install -r requirements.txt --user
+      - run:
+          name: install test-dependencies
+          command: pip3 install -r test-requirements.txt --user
       - run:
           name: confirm black version
           command: black --version
@@ -34,6 +37,9 @@ jobs:
       - run:
           name: install dependencies
           command: pip3 install -r requirements.txt --user
+      - run:
+          name: install test-dependencies
+          command: pip3 install -r test-requirements.txt --user
       - run:
           name: install pytest
           command: pip3 install pytest pytest-cov --user