add workflow to run tests

.github/workflows/test.yml

@@ -0,0 +1,42 @@
+name: Tests
+
+on:
+  push:
+    branches: [ master ]
+  pull_request:
+    branches: [ master ]
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      actions: read
+      checks: write
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Set up JDK 17
+        uses: actions/setup-java@v4
+        with:
+          java-version: '17'
+          distribution: 'temurin'
+
+      - name: Setup Gradle
+        uses: gradle/actions/setup-gradle@v4
+
+      - name: Run tests
+        run: ./gradlew test
+
+      - name: Generate test report
+        run: ./gradlew jacocoTestReport
+        if: always()
+
+      - name: Publish test results
+        uses: dorny/test-reporter@v1
+        if: always()
+        with:
+          name: Test Results
+          path: build/test-results/test/*.xml
+          reporter: java-junit

README.md

@@ -1,5 +1,7 @@
 # Gallop 🐎 XRechnung Library
 
+[![Tests](https://github.com/codebarista-de/gallop/actions/workflows/test.yml/badge.svg)](https://github.com/codebarista-de/gallop/actions/workflows/test.yml)
+
 Gallop is a Java library for creating electronic invoices (E-Invoices) compliant to
 the [XRechnung standard](https://xeinkauf.de/dokumente/).