ADD unit tests, split and refactor source code

__test__/cli.spec.js

@@ -0,0 +1,40 @@
+const cli = require('../src/cli');
+const install = require('../src/actions/install');
+
+jest.mock('../src/actions/install');
+
+describe('cli()', () => {
+  let exit;
+
+  beforeEach(() => {
+    exit = jest.fn();
+  });
+
+  it('should exit with error if not enough args are supplied', () => {
+    cli({ argv: [], exit });
+
+    expect(exit).toHaveBeenCalledWith(1);
+  });
+
+  it('should exit with error if command does not exist', () => {
+    cli({ argv: [ '/usr/local/bin/node', 'index.js', 'command' ], exit });
+
+    expect(exit).toHaveBeenCalledWith(1);
+  });
+
+  it('should exit with error if command returns error', () => {
+    install.mockImplementationOnce((cb) => cb(new Error()));
+
+    cli({ argv: [ '/usr/local/bin/node', 'index.js', 'install' ], exit });
+
+    expect(exit).toHaveBeenCalledWith(1);
+  });
+
+  it('should exit with success if command runs fine', () => {
+    install.mockImplementationOnce((cb) => cb(null));
+
+    cli({ argv: [ '/usr/local/bin/node', 'index.js', 'install' ], exit });
+
+    expect(exit).toHaveBeenCalledWith(0);
+  });
+});