Add CI testing against dev branches.

Test against the development branches of the deepcell- dependencies:
deepcell-toolbox and deepcell-tracking.

This should help catch incompatibilities between unreleased versions of
libraries in the deepcell ecosystem.

.github/workflows/tests.yaml

@@ -50,6 +50,37 @@ jobs:
       run: |
         coveralls
 
+  # A job that runs the test suite using the development version of the
+  # deepcell dependencies: deepcell-tracking and deepcell-toolbox.
+  # This ensures consistency across unreleased versions of deepcell libraries
+  test-dev:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        python-version: ["3.7", "3.8", "3.9"]
+    steps:
+      - uses: actions/checkout@v2
+
+      - name: Setup Python ${{ matrix.python-version }}
+        uses: actions/setup-python@v2
+        with:
+          python-version: ${{ matrix.python-version }}
+
+      - name: Install dependencies
+        run: |
+          python -m pip install --upgrade pip wheel setuptools
+          # Quick and dirty installation of deepcell-* dev libs
+          python -m pip install git+https://github.com/vanvalenlab/deepcell-toolbox
+          python -m pip install git+https://github.com/vanvalenlab/deepcell-tracking
+          # Install deepcell-tf from source
+          python -m pip install .
+          python -m pip install -r requirements-test.txt
+          python -m pip list
+      
+      - name: Run tests
+        run: |
+          pytest --pyargs deepcell
+
   coveralls:
     name: Finish Coveralls
     needs: tests