diff --git a/.github/testing/src/main.ts b/.github/testing/src/main.ts
index 89f36afb5bd8..0132c6b1162f 100644
--- a/.github/testing/src/main.ts
+++ b/.github/testing/src/main.ts
@@ -1,7 +1,8 @@
+import { List } from 'immutable';
 import * as affected from './affected';
 import * as git from './git';
-import {global} from './config/global';
-import {python} from './config/python';
+import { global } from './config/global';
+import { python } from './config/python';
 
 const diffsCommit =
   process.argv.length > 2 //
@@ -15,11 +16,16 @@ const baseCommit =
 
 const diffs = git.diffs(diffsCommit, baseCommit).filter(global.matchFile);
 
-const affectedPython = diffs
-  .filter(python.matchFile)
-  .map(python.changes)
-  .groupBy(change => change.package)
-  .map(change => change.map(pkg => pkg.affected))
-  .map(affected.merge);
-
-console.log('affectedPython:', affectedPython.toJS());
+const strategyMatrix = {
+  python: List(
+    diffs
+      .filter(python.matchFile)
+      .map(python.changes)
+      .groupBy(change => change.package)
+      .map(change => change.map(pkg => pkg.affected))
+      .map(affected.merge)
+      .map((tests, pkg) => ({ package: pkg, tests: tests }))
+      .values()
+  ),
+};
+console.log(JSON.stringify(strategyMatrix));
diff --git a/.github/workflows/test.yaml b/.github/workflows/test.yaml
index b3a993cfa58b..949ad45f43ad 100644
--- a/.github/workflows/test.yaml
+++ b/.github/workflows/test.yaml
@@ -24,18 +24,23 @@ jobs:
   find-tests:
     runs-on: ubuntu-latest
     outputs:
-      tests: ${{steps.affected.outputs.tests}}
+      affected: ${{steps.find-affected.outputs.affected}}
     steps:
       - uses: actions/checkout@v4
-      - id: affected
-        run: echo "tests=`TODO`" >> "$GITHUB_OUTPUT"
+      - run: npm run build
+        working-directory: .github/testing
+      - id: find-affected
+        run: echo "affected=$AFFECTED" >> "$GITHUB_OUTPUT"
+        working-directory: .github/testing
+        env:
+          AFFECTED: $(npm run affected)
+
 
   test-python:
     needs: find-tests
     runs-on: ubuntu-latest
     strategy:
-      matrix:
-        test: ${{fromJson(needs.find-tests.outputs.tests)}}
+      matrix: ${{fromJson(needs.find-tests.outputs.affected)}}
     steps:
       # - uses: actions/checkout@v4
-      - run: echo ${{matrix.test}}
+      - run: echo ${{matrix}}