Add Github action for tests

.github/workflows/elixir.yml

@@ -0,0 +1,34 @@
+name: tests
+
+on:
+  push:
+    branches: [ master ]
+  pull_request:
+    branches: [ master ]
+
+env:
+  MIX_ENV: test
+
+jobs:
+  build:
+
+    name: Build and test
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v2
+    - name: Set up Elixir
+      uses: actions/setup-elixir@v1
+      with:
+        elixir-version: '1.11.0'
+        otp-version: '23'
+    - name: Restore dependencies cache
+      uses: actions/cache@v2
+      with:
+        path: deps
+        key: ${{ runner.os }}-mix-${{ hashFiles('**/mix.lock') }}
+        restore-keys: ${{ runner.os }}-mix-
+    - name: Install dependencies
+      run: mix deps.get
+    - name: Run tests
+      run: mix test

README.md

@@ -1,5 +1,7 @@
 # Petal 🌺
 
+![tests](https://github.com/jamesduncombe/petal/workflows/tests/badge.svg)
+
 Petal is a [Bloom filter](https://en.wikipedia.org/wiki/Bloom_filter) in Elixir.
 
 Documentation can be generated with [ExDoc](https://github.com/elixir-lang/ex_doc).