Build image before testing and push at the end

Builds the image (in single arch) before testing
Loads the image into local docker (See https://github.com/docker/build-push-action#export-image-to-docker)
Rebuilds and pushes the final image in multi-arch at the end.

.github/workflows/test.yaml

@@ -24,11 +24,27 @@ env:
   PYTHONIOENCODING: "UTF-8"
 
 jobs:
-  test:
+  build-test-push:
     runs-on: ubuntu-latest
+    env:
+      DOCKER_REPO: tecnativa/docker-socket-proxy
     steps:
-      # Shared steps
-      - uses: actions/checkout@v1
+      # Prepare Docker environment and build
+      - uses: actions/checkout@v2
+      - uses: docker/setup-qemu-action@v1
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v1
+      - name: Build image(s)
+        uses: docker/build-push-action@v2
+        with:
+          context: .
+          file: ./Dockerfile
+          # HACK: Build single platform image for testing. See https://github.com/docker/buildx/issues/59
+          load: true
+          push: false
+          tags: |
+            ${{ env.DOCKER_REPO }}:local
+      # Set up and run tests
       - name: Install python
         uses: actions/setup-python@v1
         with:
@@ -51,17 +67,6 @@ jobs:
       - run: poetry install
       # Run tests
       - run: poetry run pytest
-  build-push:
-    runs-on: ubuntu-latest
-    needs: test
-    env:
-      DOCKER_REPO: tecnativa/docker-socket-proxy
-    steps:
-      # Prepare
-      - uses: actions/checkout@v2
-      - uses: docker/setup-qemu-action@v1
-      - name: Set up Docker Buildx
-        uses: docker/setup-buildx-action@v1
       # Build and push
       - name: Login to DockerHub
         uses: docker/login-action@v1
@@ -75,6 +80,9 @@ jobs:
           username: ${{ secrets.BOT_LOGIN }}
           password: ${{ secrets.BOT_TOKEN }}
       - name: Build and push
+        if:
+          github.repository == 'Tecnativa/docker-socket-proxy' && github.ref ==
+          'refs/heads/master'
         uses: docker/build-push-action@v2
         with:
           context: .

tests/conftest.py

@@ -1,4 +1,5 @@
 import json
+import os
 from contextlib import contextmanager
 from logging import info
 from pathlib import Path
@@ -7,7 +8,8 @@
 from plumbum import local
 from plumbum.cmd import docker
 
-IMAGE_NAME = "docker-socket-proxy:local"
+DOCKER_REPO = os.environ.get("DOCKER_REPO", "docker-socket-proxy")
+IMAGE_NAME = f"{DOCKER_REPO}:local"
 
 
 @pytest.fixture(autouse=True, scope="session")