added compatibility tests

* refs #665

Author: fantix

.github/workflows/test.yml

@@ -19,6 +19,7 @@ jobs:
       matrix:
         python-version: [ '3.5', '3.6', '3.7', '3.8' ]
         postgres-version: [ '9.6', '12.1' ]
+        deps-version: [ 'lowest', 'highest' ]
     services:
       postgres:
         image: fantix/postgres-ssl:${{ matrix.postgres-version }}
@@ -46,6 +47,10 @@ jobs:
       run: |
         curl -sSL https://raw.githubusercontent.com/sdispater/poetry/master/get-poetry.py | python
         $HOME/.poetry/bin/poetry install
+    - name: Use lowest dependencies versions
+      if: matrix.deps-version == 'lowest'
+      run: |
+          $HOME/.poetry/bin/poetry run pip install asyncpg==0.18 SQLAlchemy==1.3
     - name: Test with pytest
       env:
         DB_HOST: localhost