Add test for NumberFormat default minimumSignificantDigits (#864)

test/intl402/NumberFormat/default-minimum-singificant-digits.js

+// Copyright (C) 2017 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+description: Tests that the default value of minimumSignificantDigits is 1.
+esid: sec-setnfdigitoptions
+---*/
+
+// maximumSignificantDigits needs to be in range from minimumSignificantDigits
+// to 21 (both inclusive). Setting maximumSignificantDigits to 0 will throw a
+// RangeError if the (default) minimumSignificantDigits is at least 1.
+assert.throws(RangeError, function() {
+  Intl.NumberFormat(undefined, {maximumSignificantDigits: 0});
+});
+
+// If nothing is thrown, check that the options are resolved appropriately.
+var res = Intl.NumberFormat(undefined, {maximumSignificantDigits: 1})
+
+assert.sameValue(Object.getPrototypeOf(res), Intl.NumberFormat.prototype, 'result is an instance of NumberFormat')
+assert.sameValue(res.resolvedOptions().minimumSignificantDigits, 1, 'default minimumSignificantDigits')
+assert.sameValue(res.resolvedOptions().maximumSignificantDigits, 1, 'sets maximumSignificantDigits')