Speed up with pytest-split

Author: hugovk

.github/workflows/build.yml

@@ -11,12 +11,16 @@ concurrency:
 
 jobs:
   build:
-    name: ${{ matrix.image }}
+    name: ${{ matrix.image }} (shard ${{ matrix.shard }})
     runs-on: ${{ matrix.os }}
     strategy:
       fail-fast: false
       matrix:
         os: ["ubuntu-latest"]
+        # This shards every image in the matrix below. Only the valgrind
+        # image reads SHARD_INDEX/SHARD_COUNT; scope this to valgrind via
+        # `include` before re-enabling the other (fast, unsharded) images.
+        shard: [1, 2, 3, 4]
         image:
           # Run slower jobs first to give them a headstart and reduce waiting time
           - "ubuntu-26.04-resolute-ppc64le"
@@ -102,6 +106,8 @@ jobs:
           make test BRANCH=main
         env:
           DOCKER_USERNAME: ${{ secrets.DOCKER_USERNAME }}
+          SHARD_INDEX: ${{ matrix.shard }}
+          SHARD_COUNT: 4
 
       - name: Log image size
         run: |

ubuntu-24.04-noble-amd64-valgrind/Dockerfile

@@ -43,7 +43,7 @@ ARG PIP_NO_CACHE_DIR=1
 
 RUN virtualenv -p /usr/bin/python3.12-dbg --system-site-packages /vpy3 \
     && /vpy3/bin/pip install --upgrade pip \
-    && /vpy3/bin/pip install olefile pytest pytest-cov pytest-timeout pytest-valgrind \
+    && /vpy3/bin/pip install olefile pytest pytest-cov pytest-split pytest-timeout pytest-valgrind \
     && chown -R pillow:pillow /vpy3
 
 COPY depends /depends

ubuntu-24.04-noble-amd64-valgrind/Makefile

@@ -17,7 +17,7 @@ update:
 
 .PHONY: test
 test:
-	docker run --rm -e "PILLOW_VALGRIND_TEST=true" -v $(ROOT):/Pillow $(IMAGENAME):$(BRANCH)
+	docker run --rm -e "PILLOW_VALGRIND_TEST=true" -e SHARD_INDEX -e SHARD_COUNT -v $(ROOT):/Pillow $(IMAGENAME):$(BRANCH)
 
 .PHONY: push
 push:

ubuntu-24.04-noble-amd64-valgrind/test.sh

@@ -4,9 +4,14 @@ cd /Pillow
 make clean
 make install-coverage
 
+SPLIT_ARGS=""
+if [ "${SHARD_COUNT:-1}" -gt 1 ]; then
+    SPLIT_ARGS="--splits ${SHARD_COUNT} --group ${SHARD_INDEX}"
+fi
+
 PYTHONMALLOC=malloc valgrind --suppressions=/depends/python.supp --leak-check=no \
             --log-file=/tmp/valgrind-output \
-            python3 -m pytest --no-memcheck -vv --valgrind --valgrind-log=/tmp/valgrind-output
+            python3 -m pytest --no-memcheck -vv --valgrind --valgrind-log=/tmp/valgrind-output $SPLIT_ARGS
 
 # To run one test in the image:
 # make bash