feat: add artifacts and metadata outputs (#327)

Co-authored-by: CrazyMax <crazy-max@users.noreply.github.com>

__tests__/context.test.ts

@@ -0,0 +1,31 @@
+import * as os from 'os';
+import * as context from '../src/context';
+
+describe('setOutput', () => {
+  beforeEach(() => {
+    process.stdout.write = jest.fn();
+  });
+
+  it('setOutput produces the correct command', () => {
+    context.setOutput('some output', 'some value');
+    assertWriteCalls([`::set-output name=some output::some value${os.EOL}`]);
+  });
+
+  it('setOutput handles bools', () => {
+    context.setOutput('some output', false);
+    assertWriteCalls([`::set-output name=some output::false${os.EOL}`]);
+  });
+
+  it('setOutput handles numbers', () => {
+    context.setOutput('some output', 1.01);
+    assertWriteCalls([`::set-output name=some output::1.01${os.EOL}`]);
+  });
+});
+
+// Assert that process.stdout.write calls called only with the given arguments.
+function assertWriteCalls(calls: string[]): void {
+  expect(process.stdout.write).toHaveBeenCalledTimes(calls.length);
+  for (let i = 0; i < calls.length; i++) {
+    expect(process.stdout.write).toHaveBeenNthCalledWith(i + 1, calls[i]);
+  }
+}