Add tests

Closes #12

.github/workflows/deploy.yml

@@ -1,8 +1,5 @@
 name: Deploy
-on:
-  push:
-    branches:
-      - master
+on: workflow_call
 
 jobs:
   deploy:

.github/workflows/test.yml

@@ -0,0 +1,26 @@
+name: Tests
+on:
+  push:
+    branches: [master]
+  pull_request:
+    branches: [master]
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v2
+
+      - name: Install mdbook
+        run: |
+          mkdir mdbook
+          curl -sSL https://github.com/rust-lang/mdBook/releases/download/v0.4.14/mdbook-v0.4.14-x86_64-unknown-linux-gnu.tar.gz | tar -xz --directory=./mdbook
+          echo `pwd`/mdbook >> $GITHUB_PATH
+
+      - name: Run tests
+        run: mdbook test
+
+      - name: Deploy
+        if: ${{ github.event.name == 'push' }}
+        uses: ./.github/workflows/deploy.yml@master