Tests.

test/index.js

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+'use strict';
+
+var test = require('tape');
+var isSymbol = require('../index');
+
+var forEach = function (arr, func) {
+	var i;
+	for (i = 0; i < arr.length; ++i) {
+		func(arr[i], i, arr);
+	}
+};
+
+var hasSymbols = typeof Symbol === 'function' && typeof Symbol() === 'symbol';
+var debug = function (value, msg) {
+	var output = '';
+	if (hasSymbols) {
+		try { output += String(value); }
+		catch (e) { output += Symbol.prototype.toString.call(value); }
+		if (output === '') {
+			output = JSON.stringify(value);
+		}
+	}
+	var type = Object.prototype.toString.call(value).toLowerCase().slice(8, -1);
+	output += ' (' + type;
+	var typeOf = typeof value;
+	if (type !== typeOf) {
+		output += ', typeof: ' + typeOf;
+	}
+	return output + ') ' + msg;
+};
+
+test('non-symbol values', function (t) {
+	var nonSymbols = [
+		true,
+		false,
+		Object(true),
+		Object(false),
+		null,
+		undefined,
+		{},
+		[],
+		/a/g,
+		'string',
+		42,
+		new Date(),
+		function () {},
+		NaN
+	];
+	t.plan(nonSymbols.length);
+	forEach(nonSymbols, function (nonSymbol) {
+		t.equal(false, isSymbol(nonSymbol), debug(nonSymbol, 'is not a symbol'));
+	});
+	t.end();
+});
+
+test('faked symbol values', function (t) {
+	t.test('real symbol valueOf', { skip: !hasSymbols }, function (st) {
+		var fakeSymbol = { valueOf: function () { return Symbol('foo'); } };
+		st.equal(false, isSymbol(fakeSymbol), 'object with valueOf returning a symbol is not a symbol');
+		st.end();
+	});
+
+	t.test('faked @@toStringTag', { skip: !hasSymbols || !Symbol.toStringTag }, function (st) {
+		var fakeSymbol = { valueOf: function () { return Symbol('foo'); } };
+		fakeSymbol[Symbol.toStringTag] = 'Symbol';
+		st.equal(false, isSymbol(fakeSymbol), 'object with fake Symbol @@toStringTag and valueOf returning a symbol is not a symbol');
+		var notSoFakeSymbol = { valueOf: function () { return 42; } };
+		notSoFakeSymbol[Symbol.toStringTag] = 'Symbol';
+		st.equal(false, isSymbol(notSoFakeSymbol), 'object with fake Symbol @@toStringTag and valueOf not returning a symbol is not a symbol');
+		st.end();
+	});
+
+	var fakeSymbolString = { toString: function () { return 'Symbol(foo)'; } };
+	t.equal(false, isSymbol(fakeSymbolString), 'object with toString returning Symbol(foo) is not a symbol');
+
+	t.end();
+});
+
+test('Symbol support', { skip: !hasSymbols }, function (t) {
+	t.test('well-known Symbols', function (st) {
+		var wellKnownSymbols = Object.getOwnPropertyNames(Symbol).filter(function filterer(name) {
+			return name !== 'for' && name !== 'keyFor' && !(name in filterer);
+		});
+		wellKnownSymbols.forEach(function (name) {
+			var sym = Symbol[name];
+			st.equal(true, isSymbol(sym), debug(sym, ' is a symbol'));
+		});
+		st.end();
+	});
+
+	t.test('user-created symbols', function (st) {
+		var symbols = [
+			Symbol(),
+			Symbol('foo'),
+			Symbol.for('foo'),
+			Object(Symbol('object'))
+		];
+		symbols.forEach(function (sym) {
+			st.equal(true, isSymbol(sym), debug(sym, ' is a symbol'));
+		});
+		st.end();
+	});
+
+	t.end();
+});
+