test: add test description to fs.readFile tests

PR-URL: https://github.com/nodejs/node/pull/17610
Refs: https://github.com/nodejs/node/pull/17054#discussion_r155406755
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Evan Lucas <evanlucas@me.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>
Reviewed-By: Jon Moss <me@jonathanmoss.me>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>

test/parallel/test-fs-readfile-empty.js

@@ -21,6 +21,9 @@
 
 'use strict';
 require('../common');
+
+// Trivial test of fs.readFile on an empty file.
+
 const assert = require('assert');
 const fs = require('fs');
 const fixtures = require('../common/fixtures');

test/parallel/test-fs-readfile-error.js

@@ -21,6 +21,9 @@
 
 'use strict';
 const common = require('../common');
+
+// Test that fs.readFile fails correctly on a non-existent file.
+
 // `fs.readFile('/')` does not fail on FreeBSD, because you can open and read
 // the directory there.
 if (common.isFreeBSD)

test/parallel/test-fs-readfile-fd.js

@@ -1,5 +1,8 @@
 'use strict';
 require('../common');
+
+// Test fs.readFile using a file descriptor.
+
 const fixtures = require('../common/fixtures');
 const assert = require('assert');
 const fs = require('fs');

test/parallel/test-fs-readfile-unlink.js

@@ -21,6 +21,9 @@
 
 'use strict';
 const common = require('../common');
+
+// Test that unlink succeeds immediately after readFile completes.
+
 const assert = require('assert');
 const fs = require('fs');
 const path = require('path');

test/parallel/test-fs-readfile-zero-byte-liar.js

@@ -21,6 +21,9 @@
 
 'use strict';
 const common = require('../common');
+
+// Test that readFile works even when stat returns size 0.
+
 const assert = require('assert');
 const fs = require('fs');