ci: Add coverage report

Author: dhl

.github/workflows/test.yml

@@ -0,0 +1,28 @@
+name: Run tests and upload coverage
+
+on:
+  push
+
+jobs:
+  coverage:
+    name: Report coverage
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+
+      - name: Set up Node
+        uses: actions/setup-node@v4
+
+      - name: Install dependencies
+        run: npm install
+
+      - name: Run tests
+        run: npm run coverage
+
+      - name: Upload results to Codecov
+        uses: codecov/codecov-action@v4
+        with:
+          token: ${{ secrets.CODECOV_TOKEN }}

README.md

@@ -1,5 +1,7 @@
 # blake2b-solidity
 
+[![codecov](https://codecov.io/github/dhl/blake2b-solidity/graph/badge.svg?token=4WOC5GEC7H)](https://codecov.io/github/dhl/blake2b-solidity)
+
 `blake2b-solidity` is a high-performance Solidity implementation of the [BLAKE2b](https://www.blake2.net/) hash
 function.