add tests to cover almost every cli parsing case and add docs info for

`command --help`

__tests__/fixtures/index/run-version/package.json

@@ -0,0 +1,5 @@
+{
+  "name": "test_add",
+  "version": "1.0.0",
+  "license": "UNLICENSED"
+}

__tests__/index.js

@@ -3,6 +3,7 @@
 import NoopReporter from '../src/reporters/base-reporter.js';
 import makeTemp from './_temp';
 import * as fs from '../src/util/fs.js';
+const pkg = require('../package.json');
 
 const path = require('path');
 const exec = require('child_process').exec;
@@ -37,40 +38,68 @@ Promise<Array<?string>> {
   });
 }
 
-test.concurrent('should add package', async () => {
-  const stdout = await execCommand('add', ['left-pad'], 'run-add', true);
+function expectAddSuccessfullOutput(stdout, pkg) {
   const lastLines = stdout.slice(stdout.length - 4);
   expect(lastLines[0]).toEqual('success Saved lockfile.');
   expect(lastLines[1]).toEqual('success Saved 1 new dependency.');
-  expect(lastLines[2]).toMatch(/left-pad/);
-  expect(lastLines[3]).toMatch(/^Done/);
+  expect(lastLines[2]).toContain(pkg);
+  expect(lastLines[3]).toContain('Done');
+}
+
+function expectAddSuccessfullOutputWithNoLockFile(stdout, pkg) {
+  const lastLines = stdout.slice(stdout.length - 4);
+  expect(lastLines[1]).toEqual('success Saved 1 new dependency.');
+  expect(lastLines[2]).toContain(pkg);
+  expect(lastLines[3]).toContain('Done');
+}
+
+function expectRunOutput(stdout) {
+  const lastLines = stdout.slice(stdout.length - 2);
+  expect(lastLines[0]).toMatch(/A message from custom script/);
+  expect(lastLines[1]).toMatch(/^Done/);
+}
+
+function expectHelpOutput(stdout) {
+  expect(stdout[0]).toEqual('Usage: yarn [command] [flags]');
+  const lastLines = stdout.slice(stdout.length - 2);
+  expect(lastLines[0]).toEqual('Run `yarn help COMMAND` for more information on specific commands.');
+  expect(lastLines[1]).toEqual('Visit https://yarnpkg.com/en/docs/cli/ to learn more about Yarn.');
+}
+
+function expectHelpOutputAsSubcommand(stdout) {
+  expect(stdout[0]).toEqual('Usage: yarn add [packages ...] [flags]');
+  expect(stdout[stdout.length - 1])
+    .toEqual('Visit https://yarnpkg.com/en/docs/cli/add for documentation about this command.');
+}
+
+function expectAnErrorMessage(command: Promise<Array<?string>>, error: string) : Promise<void> {
+  return command.catch((reason) =>
+    expect(reason.message).toContain(error),
+  );
+}
+
+function expectInstallOutput(stdout) {
+  expect(stdout[0]).toEqual(`yarn install v${pkg.version}`);
+}
+
+test.concurrent('should add package', async () => {
+  const stdout = await execCommand('add', ['left-pad'], 'run-add', true);
+  expectAddSuccessfullOutput(stdout, 'left-pad');
 });
 
 test.concurrent('should add package with no-lockfile option', async () => {
   const stdout = await execCommand('add', ['repeating', '--no-lockfile'], 'run-add-option', true);
-  const lastLines = stdout.slice(stdout.length - 4);
-  expect(lastLines[0]).not.toMatch(/Saved lockfile/);
-  expect(lastLines[1]).toEqual('success Saved 1 new dependency.');
-  expect(lastLines[2]).toMatch(/repeating/);
-  expect(lastLines[3]).toMatch(/^Done/);
+  expectAddSuccessfullOutputWithNoLockFile(stdout, 'repeating');
 });
 
 test.concurrent('should add package with no-lockfile option in front', async () => {
   const stdout = await execCommand('add', ['--no-lockfile', 'split-lines'], 'run-add-option-in-front', true);
-  const lastLines = stdout.slice(stdout.length - 4);
-  expect(lastLines[0]).not.toMatch(/Saved lockfile/);
-  expect(lastLines[1]).toEqual('success Saved 1 new dependency.');
-  expect(lastLines[2]).toMatch(/split-lines/);
-  expect(lastLines[3]).toMatch(/^Done/);
+  expectAddSuccessfullOutputWithNoLockFile(stdout, 'split-lines');
 });
 
 test.concurrent('should add lockfile package', async () => {
   const stdout = await execCommand('add', ['lockfile'], 'run-add-lockfile', true);
-  const lastLines = stdout.slice(stdout.length - 4);
-  expect(lastLines[0]).toEqual('success Saved lockfile.');
-  expect(lastLines[1]).toEqual('success Saved 1 new dependency.');
-  expect(lastLines[2]).toMatch(/lockfile/);
-  expect(lastLines[3]).toMatch(/^Done/);
+  expectAddSuccessfullOutput(stdout, 'lockfile');
 });
 
 test.concurrent('should add progress package globally', async () => {
@@ -85,24 +114,79 @@ test.concurrent('should add progress package globally', async () => {
 
 test.concurrent('should run custom script', async () => {
   const stdout = await execCommand('run', ['custom-script'], 'run-custom-script');
-  const lastLines = stdout.slice(stdout.length - 2);
-  expect(lastLines[0]).toMatch(/A message from custom script/);
-  expect(lastLines[1]).toMatch(/^Done/);
+  expectRunOutput(stdout);
 });
 
 test.concurrent('should run custom script without run command', async () => {
   const stdout = await execCommand('custom-script', [], 'run-custom-script');
-  const lastLines = stdout.slice(stdout.length - 2);
-  expect(lastLines[0]).toMatch(/A message from custom script/);
-  expect(lastLines[1]).toMatch(/^Done/);
+  expectRunOutput(stdout);
 });
 
 test.concurrent('should run help command', async () => {
   const stdout = await execCommand('help', [], 'run-help');
-  expect(stdout[0]).toEqual('Usage: yarn [command] [flags]');
+  expectHelpOutput(stdout);
+});
+
+test.concurrent('should run help command with --help', async () => {
+  const stdout = await execCommand('--help', [], 'run-help');
+  expectHelpOutput(stdout);
+});
+
+test.concurrent('should run help command with -h', async () => {
+  const stdout = await execCommand('-h', [], 'run-help');
+  expectHelpOutput(stdout);
 });
 
 test.concurrent('should run add command with help option', async () => {
   const stdout = await execCommand('add', ['--help'], 'run-help');
-  expect(stdout[0]).toEqual('Usage: yarn add [packages ...] [flags]');
+  expectHelpOutputAsSubcommand(stdout);
+});
+
+test.concurrent('should run help command with add option', async () => {
+  const stdout = await execCommand('help', ['add'], 'run-help');
+  expectHelpOutputAsSubcommand(stdout);
+});
+
+test.concurrent('should run --help command with add option', async () => {
+  const stdout = await execCommand('--help', ['add'], 'run-help');
+  expectHelpOutputAsSubcommand(stdout);
+});
+
+test.concurrent('should run -h command with add option', async () => {
+  const stdout = await execCommand('-h', ['add'], 'run-help');
+  expectHelpOutputAsSubcommand(stdout);
+});
+
+test.concurrent('should ignore all arguments after --', async () => {
+  const stdout = await execCommand('help', ['--', 'add'], 'run-help');
+  expectHelpOutput(stdout);
+});
+
+test.concurrent('should run version command', async () => {
+  await expectAnErrorMessage(
+    execCommand('version', [], 'run-version'),
+    'Can\'t answer a question unless a user TTY',
+  );
+});
+
+test.concurrent('should run --version command with --version', async () => {
+  const stdout = await execCommand('--version', [], 'run-version');
+  expect(stdout[0]).toEqual(pkg.version);
+});
+
+test.concurrent('should install if no args', async () => {
+  const stdout = await execCommand('', [], 'run-add', true);
+  expectInstallOutput(stdout);
+});
+
+test.concurrent('should install if first arg looks like a flag', async () => {
+  const stdout = await execCommand('--offline', [], 'run-add', true);
+  expectInstallOutput(stdout);
+});
+
+test.concurrent('should interpolate aliases', async () => {
+  await expectAnErrorMessage(
+    execCommand('i', [], 'run-add', true),
+    'Did you mean `yarn install`?',
+  );
 });

src/cli/index.js

@@ -171,6 +171,9 @@ if (commandName === 'help' || args.indexOf('--help') >= 0 || args.indexOf('-h')
       console.log();
     });
   }
+  if (commandName !== 'help') {
+    commander.on('--help', () => console.log('  ' + getDocsInfo(commandName) + '\n'));
+  }
 
   commander.parse(startArgs.concat(args));
   commander.help();