Add GitHub Actions to run tests (#130)

There are two separate actions - one for the mandatory tests, and one
for the extra tests which is only run if any extra tests were modified.

Author: illicitonion

.github/workflows/extra-tests.yml

@@ -0,0 +1,14 @@
+name: Run extra tests
+on:
+  pull_request:
+    paths:
+      - extra/**
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v2
+    - name: Install modules
+      run: npm install
+    - name: Run extra tests
+      run: npm run extra-tests

.github/workflows/mandatory-tests.yml

@@ -0,0 +1,11 @@
+name: Run mandatory tests
+on: pull_request
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v2
+    - name: Install modules
+      run: npm install
+    - name: Run mandatory tests
+      run: npm test