Add tests for System model

src/model/system.test.js

@@ -0,0 +1,45 @@
+import * as core from '@actions/core';
+import System from './system';
+
+const info = jest.spyOn(core, 'info').mockImplementation(() => {});
+
+afterEach(() => {
+  jest.clearAllMocks();
+});
+
+describe('System', () => {
+  describe('run', () => {
+    it('runs a command successfully', async () => {
+      await expect(System.run('true')).resolves.not.toBeNull();
+    });
+
+    it('outputs results', async () => {
+      await expect(System.run('echo test')).resolves.toStrictEqual('test\n');
+    });
+
+    it('throws on when error code is not 0', async () => {
+      await expect(System.run('false')).rejects.toThrowError();
+    });
+
+    it('throws when no arguments are given', async () => {
+      await expect(System.run()).rejects.toThrowError();
+    });
+
+    it('outputs info', async () => {
+      await expect(System.run('echo test')).resolves.not.toBeNull();
+      expect(info).toHaveBeenLastCalledWith('test\n');
+    });
+
+    it('outputs info only once', async () => {
+      await expect(System.run('echo 1')).resolves.not.toBeNull();
+      expect(info).toHaveBeenCalledTimes(1);
+      expect(info).toHaveBeenLastCalledWith('1\n');
+
+      info.mockClear();
+      await expect(System.run('echo 2')).resolves.not.toBeNull();
+      await expect(System.run('echo 3')).resolves.not.toBeNull();
+      expect(info).toHaveBeenCalledTimes(2);
+      expect(info).toHaveBeenLastCalledWith('3\n');
+    });
+  });
+});