Add codecov support

.github/workflows/test.yml

@@ -30,4 +30,7 @@ jobs:
         run: yarn install --frozen-lockfile
 
       - name: Run jest
-        run: npx jest --coverage=false
+        run: npx jest
+
+      - name: Upload coverage
+        uses: codecov/codecov-action@v1

codecov.yml

@@ -0,0 +1,10 @@
+coverage:
+  status:
+    project:
+      default:
+        threshold: 1%
+        if_not_found: success # no commit found? still set a success
+    patch:
+      default:
+        threshold: 1%
+        if_not_found: success