Best JavaScript code snippet using jest
arguments-apply.js
Source: arguments-apply.js
1// Copyright 2009 the V8 project authors. All rights reserved.2// Redistribution and use in source and binary forms, with or without3// modification, are permitted provided that the following conditions are4// met:5//6// * Redistributions of source code must retain the above copyright7// notice, this list of conditions and the following disclaimer.8// * Redistributions in binary form must reproduce the above9// copyright notice, this list of conditions and the following10// disclaimer in the documentation and/or other materials provided11// with the distribution.12// * Neither the name of Google Inc. nor the names of its13// contributors may be used to endorse or promote products derived14// from this software without specific prior written permission.15//16// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS17// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT18// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR19// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT20// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,21// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT22// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,23// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY24// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT25// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE26// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.27function ReturnArguments() {28 return arguments;29}30function ReturnReceiver() {31 return this;32}33function Global() {34 return ReturnArguments.apply(this, arguments);35}36assertEquals(0, Global().length);37assertEquals(1, Global(1).length);38assertEquals(2, Global(2)[0]);39assertEquals(2, Global(3, 4).length);40assertEquals(3, Global(3, 4)[0]);41assertEquals(4, Global(3, 4)[1]);42function Local() {43 var object = { f: ReturnArguments };44 return object.f.apply(this, arguments);45}46assertEquals(0, Local().length);47assertEquals(1, Local(1).length);48assertEquals(2, Local(2)[0]);49assertEquals(2, Local(3, 4).length);50assertEquals(3, Local(3, 4)[0]);51assertEquals(4, Local(3, 4)[1]);52function ShadowArguments() {53 var arguments = [3, 4];54 return ReturnArguments.apply(this, arguments);55}56assertEquals(2, ShadowArguments().length);57assertEquals(3, ShadowArguments()[0]);58assertEquals(4, ShadowArguments()[1]);59function NonObjectReceiver(receiver) {60 return ReturnReceiver.apply(receiver, arguments);61}62assertEquals(Object(42), NonObjectReceiver(42));63assertEquals("object", typeof NonObjectReceiver(42));64assertInstanceof(NonObjectReceiver(42), Number);65assertSame(this, NonObjectReceiver(null));66assertSame(this, NonObjectReceiver(void 0));67function FunctionReceiver() {68 return ReturnReceiver.apply(Object, arguments);69}70assertTrue(Object === FunctionReceiver());71function ShadowApply() {72 function f() { return 42; }73 f.apply = function() { return 87; }74 return f.apply(this, arguments);75}76assertEquals(87, ShadowApply());77assertEquals(87, ShadowApply(1));78assertEquals(87, ShadowApply(1, 2));79function CallNonFunction() {80 var object = { apply: Function.prototype.apply };81 return object.apply(this, arguments);82}83assertThrows(CallNonFunction, TypeError);84// Make sure that the stack after the apply optimization is85// in a valid state.86function SimpleStackCheck() {87 var sentinel = 42;88 var result = ReturnArguments.apply(this, arguments);89 assertTrue(result != null);90 assertEquals(42, sentinel);91}92SimpleStackCheck();93function ShadowArgumentsWithConstant() {94 var arguments = null;95 return ReturnArguments.apply(this, arguments);96}97assertEquals(0, ShadowArgumentsWithConstant().length);98assertEquals(0, ShadowArgumentsWithConstant(1).length);99assertEquals(0, ShadowArgumentsWithConstant(1, 2).length);100// Make sure we can deal with unfolding lots of arguments on the101// stack even in the presence of the apply optimizations.102var array = new Array(2048);...
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Since Jest tests are runtime tests, they only have access to runtime information. You're trying to use a type, which is compile-time information. TypeScript should already be doing the type aspect of this for you. (More on that in a moment.)
The fact the tests only have access to runtime information has a couple of ramifications:
If it's valid for getAll
to return an empty array (because there aren't any entities to get), the test cannot tell you whether the array would have had Entity
elements in it if it hadn't been empty. All it can tell you is it got an array.
In the non-empty case, you have to check every element of the array to see if it's an Entity
. You've said Entity
is a class, not just a type, so that's possible. I'm not a user of Jest (I should be), but it doesn't seem to have a test specifically for this; it does have toBeTruthy
, though, and we can use every
to tell us if every element is an Entity
:
it('should return an array of Entity class', async () => {
const all = await service.getAll()
expect(all.every(e => e instanceof Entity)).toBeTruthy();
});
Beware, though, that all calls to every
on an empty array return true
, so again, that empty array issue raises its head.
If your Jest tests are written in TypeScript, you can improve on that by ensuring TypeScript tests the compile-time type of getAll
's return value:
it('should return an array of Entity class', async () => {
const all: Entity[] = await service.getAll()
// ^^^^^^^^^^
expect(all.every(e => e instanceof Entity)).toBeTruthy();
});
TypeScript will complain about that assignment at compile time if it's not valid, and Jest will complain at runtime if it sees an array containing a non-Entity
object.
But jonrsharpe has a good point: This test may not be useful vs. testing for specific values that should be there.
Check out the latest blogs from LambdaTest on this topic:
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|<p>it('check_object_of_Car', () => {</p><p>
expect(newCar()).toBeInstanceOf(Car);</p><p>
});</p>|
| :- |
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