Create test stub, add CI workflow file, add test badge

.github/workflows/ci.yml

@@ -0,0 +1,15 @@
+name: "Tests"
+
+on:
+  pull_request:
+  push:
+    branches:         # array of glob patterns matching against refs/heads. Optional; defaults to all
+      - master          # triggers on pushes that contain changes in master
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v1
+      - run: npm ci
+      - run: npm test

README.md

@@ -1,7 +1,7 @@
 # GitHub Action - Releases API
 This GitHub Action (written in JavaScript) wraps the [GitHub Release API](https://developer.github.com/v3/repos/releases/), specifically the [Upload a Release Asset](https://developer.github.com/v3/repos/releases/#upload-a-release-asset) endpoint, to allow you to leverage GitHub Actions to upload release assets.
 
-<a href="https://github.com/actions/upload-release-asset"><img alt="GitHub Actions status" src="https://github.com/actions/upload-release-asset/workflows/Upload%20Release%20Asset/badge.svg"></a>
+<a href="https://github.com/actions/upload-release-asset"><img alt="GitHub Actions status" src="https://github.com/actions/upload-release-asset/workflows/Tests/badge.svg"></a>
 
 ## Usage
 ### Pre-requisites

tests/main.test.js

@@ -0,0 +1,37 @@
+jest.mock('@actions/github');
+
+const { GitHub, context } = require('@actions/github');
+const run = require('../src/main.js');
+
+/* eslint-disable no-undef */
+describe('module', () => {
+    let uploadReleaseAsset;
+
+    beforeEach(() => {
+        uploadReleaseAsset = jest.fn();
+
+        context.repo = {
+            owner: 'owner',
+            repo: 'repo'
+        };
+
+        const github = {
+            repos: {
+                uploadReleaseAsset
+            }
+        };
+
+        GitHub.mockImplementation(() => github);
+    });
+
+    test('Upload release endpoint is called', async () => {
+        await run();
+
+        expect(uploadReleaseAsset).toHaveBeenCalledWith({
+            owner: 'owner',
+            repo: 'repo'
+        });
+    });
+
+    test('Outputs are set', async () => {});
+});