Creates tests-only branch

- Removes all source code
- Pip-installs latest pip version of UEDGE for testing
- Moves tests to root

.github/workflows/tests.yml

@@ -14,9 +14,9 @@ jobs:
         python-version: [3.9]
 
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v4
     - name: Set up Python ${{ matrix.python-version }}
-      uses: actions/setup-python@v2
+      uses: actions/setup-python@v4
       with:
         python-version: ${{ matrix.python-version }}
     - name: Install pip dependencies
@@ -25,11 +25,21 @@ jobs:
         python -m pip install forthon mppl numpy h5py
         python -m pip install flake8
         python -m pip install pytest-isolate pytest-xdist
+    - name: Checkout develop branch
+      uses: actions/checkout@v4
+      with:
+        ref: develop
+        repository: LLNL/UEDGE 
     - name: Build UEDGE
       run: |
         python setup.py build
         python setup.py install
+    - name: Return to pytests branch
+      uses: actions/checkout@v4
+      with:
+        ref: pytests
+        repository: LLNL/UEDGE 
     - name: Test with pytest
       run: |
         # Create a clean UEDGE instance for every test
-        pytest --isolate --tb=native pytests/pytests
+        pytest --isolate --tb=native pytests