Use github actions for testing code

.github/workflows/run_tests.yml

@@ -0,0 +1,35 @@
+name: Run tests
+
+on: [push]
+
+jobs:
+    all:
+        runs-on: ubuntu-latest
+        env:
+            CI: true
+        steps:
+            - uses: actions/checkout@v1
+            - name: Use Node.js 12.x
+              uses: actions/setup-node@v1
+              with:
+                  node-version: 12.x
+            - name: Get yarn cache
+              id: yarn-cache
+              run: echo "::set-output name=dir::$(yarn cache dir)"
+            - uses: actions/cache@v1
+              with:
+                  path: ${{ steps.yarn-cache.outputs.dir }}
+                  key: ${{ runner.os }}-yarn-${{ hashFiles('**/yarn.lock') }}
+                  restore-keys: |
+                      ${{ runner.os }}-yarn-
+            - name: Cache node modules
+              uses: actions/cache@v1
+              with:
+                  path: node_modules
+                  key: ${{ runner.OS }}-build-${{ hashFiles('**/yarn.lock') }}
+                  restore-keys: |
+                      ${{ runner.OS }}-node_modules-
+            - name: yarn install
+              run: yarn install
+            - name: typecheck
+              run: yarn test