docs:update PR template.

.github/PULL_REQUEST_TEMPLATE.md

@@ -21,7 +21,7 @@ fixes #
 
 ## Checklist
 
-- [ ] Add junit tests for adding or updating code.
+- [ ] Coverage from `Codecov Report` should not decrease (which means adding junit tests for adding or updating code).
 - [ ] All junit tests passing.
 - [ ] Add copyright holder at the beginning of .java file if it is new.
 - [ ] Add information of this PR to CHANGELOG.md in root of project.

.github/workflows/codecov.yml

@@ -0,0 +1,34 @@
+name: Codecov
+
+on:
+  push:
+    branches:
+      - hoxton
+      - 2021.0
+      - 2020.0
+      - greenwich
+  pull_request:
+    branches:
+      - hoxton
+      - 2021.0
+      - 2020.0
+      - greenwich
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout codes
+        uses: actions/checkout@v3
+      - name: Set up JDK 8
+        uses: actions/setup-java@v3
+        with:
+          distribution: 'temurin'
+          java-version: 8
+      - name: Test with Maven
+        run: mvn -B test --file pom.xml
+      - name: Upload coverage to Codecov
+        uses: codecov/codecov-action@v3
+        with:
+          file: ${{ github.workspace }}/target/site/jacoco/jacoco.xml