test: add e2e tests for docker-build-push workflow

- test-docker-workflow-outputs.sh: validates workflow defines required
  outputs (digest, tags, sbom-path), uses correct metadata and build
  actions, supports cosign signing and SBOM generation
- test.yaml: GitHub Actions workflow to run tests on changes

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: samuelho-dev

.github/workflows/test.yaml

@@ -0,0 +1,25 @@
+name: Test Reusable Workflows
+
+on:
+  push:
+    branches: [main]
+    paths:
+      - '.github/workflows/**'
+      - 'tests/**'
+  pull_request:
+    branches: [main]
+    paths:
+      - '.github/workflows/**'
+      - 'tests/**'
+
+jobs:
+  test-workflow-outputs:
+    name: Test Docker Workflow Outputs
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Run workflow output tests
+        run: |
+          chmod +x tests/test-docker-workflow-outputs.sh
+          ./tests/test-docker-workflow-outputs.sh

tests/test-docker-workflow-outputs.sh

@@ -0,0 +1,128 @@
+#!/usr/bin/env bash
+# Unit test for docker-build-push workflow output format
+# Tests that the workflow outputs meet expected format for downstream consumers
+set -euo pipefail
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+WORKFLOW_FILE="${SCRIPT_DIR}/../.github/workflows/docker-build-push.yml"
+
+echo "=== git-flow: Docker Build Workflow Output Tests ==="
+echo ""
+
+TESTS_PASSED=0
+TESTS_FAILED=0
+
+# Helper functions
+pass() {
+  echo "PASS: $1"
+  TESTS_PASSED=$((TESTS_PASSED + 1))
+}
+
+fail() {
+  echo "FAIL: $1"
+  TESTS_FAILED=$((TESTS_FAILED + 1))
+}
+
+# Test 1: Workflow file exists
+echo "Test 1: Workflow file exists"
+if [[ -f "$WORKFLOW_FILE" ]]; then
+  pass "Workflow file found at $WORKFLOW_FILE"
+else
+  fail "Workflow file not found at $WORKFLOW_FILE"
+  exit 1
+fi
+
+# Test 2: Workflow defines 'digest' output
+echo ""
+echo "Test 2: Workflow defines 'digest' output"
+if grep -q "^[[:space:]]*digest:" "$WORKFLOW_FILE"; then
+  pass "Workflow defines 'digest' output"
+else
+  fail "Workflow missing 'digest' output definition"
+fi
+
+# Test 3: Workflow defines 'tags' output
+echo ""
+echo "Test 3: Workflow defines 'tags' output"
+if grep -q "^[[:space:]]*tags:" "$WORKFLOW_FILE"; then
+  pass "Workflow defines 'tags' output"
+else
+  fail "Workflow missing 'tags' output definition"
+fi
+
+# Test 4: Workflow defines 'sbom-path' output
+echo ""
+echo "Test 4: Workflow defines 'sbom-path' output"
+if grep -q "^[[:space:]]*sbom-path:" "$WORKFLOW_FILE"; then
+  pass "Workflow defines 'sbom-path' output"
+else
+  fail "Workflow missing 'sbom-path' output definition"
+fi
+
+# Test 5: Digest output comes from build step
+echo ""
+echo "Test 5: Digest output sources from build step"
+if grep -q 'digest:.*\${{ steps.build.outputs.digest }}' "$WORKFLOW_FILE"; then
+  pass "Digest output correctly sourced from build step"
+else
+  fail "Digest output not correctly sourced from build step"
+fi
+
+# Test 6: Tags output comes from meta step
+echo ""
+echo "Test 6: Tags output sources from meta step"
+if grep -q 'tags:.*\${{ steps.meta.outputs.tags }}' "$WORKFLOW_FILE"; then
+  pass "Tags output correctly sourced from meta step"
+else
+  fail "Tags output not correctly sourced from meta step"
+fi
+
+# Test 7: Workflow uses docker/metadata-action for consistent tagging
+echo ""
+echo "Test 7: Uses docker/metadata-action for tag generation"
+if grep -q "docker/metadata-action" "$WORKFLOW_FILE"; then
+  pass "Uses docker/metadata-action for consistent tagging"
+else
+  fail "Missing docker/metadata-action for tag generation"
+fi
+
+# Test 8: Workflow uses docker/build-push-action
+echo ""
+echo "Test 8: Uses docker/build-push-action"
+if grep -q "docker/build-push-action" "$WORKFLOW_FILE"; then
+  pass "Uses docker/build-push-action"
+else
+  fail "Missing docker/build-push-action"
+fi
+
+# Test 9: Workflow supports cosign signing
+echo ""
+echo "Test 9: Supports cosign image signing"
+if grep -q "sigstore/cosign-installer" "$WORKFLOW_FILE"; then
+  pass "Supports cosign image signing"
+else
+  fail "Missing cosign signing support"
+fi
+
+# Test 10: Workflow generates SBOM
+echo ""
+echo "Test 10: Generates SBOM with anchore/sbom-action"
+if grep -q "anchore/sbom-action" "$WORKFLOW_FILE"; then
+  pass "Generates SBOM with anchore/sbom-action"
+else
+  fail "Missing SBOM generation"
+fi
+
+echo ""
+echo "=== Test Results ==="
+echo "Passed: $TESTS_PASSED"
+echo "Failed: $TESTS_FAILED"
+echo ""
+
+if [[ $TESTS_FAILED -gt 0 ]]; then
+  echo "FAILED: Some tests did not pass"
+  exit 1
+else
+  echo "SUCCESS: All tests passed"
+  exit 0
+fi