intl: increase coverage for NumberFormat

Increase coverage for Intl.NumberFormat by adding a test for format
checking it's default value.

test/intl402/NumberFormat/prototype/format/default-value.js

@@ -0,0 +1,43 @@
+// Copyright (C) 2018 Ujjwal Sharma. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-number-format-functions
+description: >
+  Tests that the default value for the argument of
+  Intl.NumberFormat.prototype.format (value) is undefined.
+info: |
+  11.1.4Number Format Functions
+
+  3. If value is not provided, let value be undefined.
+---*/
+
+const localesList = [
+  undefined,
+  ['de'],
+  ['th-u-nu-thai'],
+  ['en'],
+  ['ja-u-nu-jpanfin'],
+  ['ar-u-nu-arab']
+];
+const optionsList = [
+  undefined,
+  { style: 'percent' },
+  { style: 'currency', currency: 'EUR', currencyDisplay: 'symbol' },
+  { style: 'currency', currency: 'IQD', currencyDisplay: 'symbol' },
+  { style: 'currency', currency: 'KMF', currencyDisplay: 'symbol' },
+  { style: 'currency', currency: 'CLF', currencyDisplay: 'symbol' },
+  {
+    useGrouping: false,
+    minimumIntegerDigits: 3,
+    minimumFractionDigits: 1,
+    maximumFractionDigits: 3
+  }
+];
+
+localesList.forEach(locales => {
+  optionsList.forEach(options => {
+    const nf = Intl.NumberFormat(locales, options);
+    assert.sameValue(nf.format(), nf.format(undefined));
+  });
+});