test: write test case for --help flag

Author: jamesgeorge007

e2e/index.js

@@ -8,5 +8,10 @@ const rootCommand = path.join(process.cwd(), 'bin/docsify');
 
 test('shows up help message without any args', async t => {
     const { stderr } = await execa(rootCommand, {reject: false});
-    t.snapshot(stderr)
+    t.snapshot(stderr);
+});
+
+test('shows up help message by passing in --help flag', async t => {
+    const { stdout } = await execa(rootCommand, ['--help']);
+    t.snapshot(stdout);
 });

e2e/index.js.md

@@ -4,6 +4,28 @@ The actual snapshot is saved in `index.js.snap`.
 
 Generated by [AVA](https://ava.li).
 
+## shows up help message by passing in --help flag
+
+> Snapshot 1
+
+    `Usage: docsify <init|serve> <path>␊
+    ␊
+    Commands:␊
+      docsify init [path]   Creates new docs␊
+      docsify serve [path]  Run local server to preview site.␊
+      docsify start <path>  Server for SSR␊
+    ␊
+    Global Options␊
+      --help, -h     Show help                                             [boolean]␊
+      --version, -v  Show version number                                   [boolean]␊
+    ␊
+    Documentation:␊
+      https://docsifyjs.github.io/docsify␊
+      https://docsifyjs.github.io/docsify-cli␊
+    ␊
+    Development:␊
+      https://github.com/docsifyjs/docsify-cli/blob/master/CONTRIBUTING.md`
+
 ## shows up help message without any args
 
 > Snapshot 1