changeListener.test.js
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changeListener.test.js
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	import registerChangeListener from '../../src/changeListener';

	const stubStore = ( () => {
	let state;

	return {
	getState() {
	return state;
	},
	setState( value ) {
	state = value;
	}
	};
	} )();

	QUnit.module( 'ext.popups/changeListener' );

	QUnit.test( 'it should only call the callback when the state has changed', function ( assert ) {
	const spy = this.sandbox.spy();
	let boundChangeListener;

	stubStore.subscribe = ( changeListener ) => {
	boundChangeListener = changeListener;
	};

	registerChangeListener( stubStore, spy );

	stubStore.setState( {} );

	if ( !boundChangeListener ) {
	assert.true( false, 'The change listener was not bound.' );
	}
	boundChangeListener();
	boundChangeListener();

	assert.strictEqual( spy.callCount, 1, 'The spy was called once.' );
	assert.true(
	spy.calledWith(
	undefined, // The initial internal state of the change listener.
	{}
	),
	'The spy was called with the correct arguments.'
	);

	stubStore.setState( {
	foo: 'bar'
	} );

	boundChangeListener();

	assert.strictEqual( spy.callCount, 2, 'The spy was called twice.' );
	assert.true(
	spy.calledWith(
	{},
	{
	foo: 'bar'
	}
	),
	'The spy was called with the correct arguments.'
	);
	} );