test: add tests for unixtimestamp generation

This test checks for the different input types for the generation
of UNIX timestamps in the fs module.

PR-URL: https://github.com/nodejs/node/pull/11886
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

test/parallel/test-fs-timestamp-parsing-error.js

@@ -0,0 +1,16 @@
+'use strict';
+require('../common');
+const assert = require('assert');
+const fs = require('fs');
+
+[undefined, null, []].forEach((input) => {
+  assert.throws(() => fs._toUnixTimestamp(input),
+                new RegExp('^Error: Cannot parse time: ' + input + '$'));
+});
+
+assert.throws(() => fs._toUnixTimestamp({}),
+              /^Error: Cannot parse time: \[object Object\]$/);
+
+[1, '1', Date.now(), -1, '-1', Infinity].forEach((input) => {
+  assert.doesNotThrow(() => fs._toUnixTimestamp(input));
+});