Add a test_build phase to ensure produced output is working

.github/workflows/build.yml

@@ -32,6 +32,11 @@ jobs:
       run: |
         pipenv run pytest --cov=fastapi_users/
         pipenv run codecov
+    - name: Build and install it on system host
+      run: |
+        pipenv run flit build
+        pipenv run flit install --python $(which python)
+        python test_build.py
 
   release:
     runs-on: ubuntu-latest

setup.cfg

@@ -17,7 +17,8 @@ ignore = D1
 profile = black
 
 [tool:pytest]
-markers = 
+addopts = --ignore=test_build.py
+markers =
 	authentication
 	db
 	fastapi_users

test_build.py

@@ -0,0 +1,9 @@
+# flake8: noqa
+import sys
+
+try:
+    from fastapi_users import FastAPIUsers
+except:
+    sys.exit(1)
+
+sys.exit(0)