liza/test/store/MissLookupTest.js

/**
 * Test case for Cascading store
 *
 *  Copyright (C) 2016 LoVullo Associates, Inc.
 *
 *  This file is part of the Liza Data Collection Framework
 *
 *  Liza is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

"use strict";

var Class  = require( 'easejs' ).Class,
    store  = require( '../../' ).store,
    chai   = require( 'chai' ),
    expect = chai.expect,
    Store  = store.MemoryStore,
    Sut    = store.MissLookup;

chai.use( require( 'chai-as-promised' ) );

const StubStore = Class.extend( Store,
{
    'virtual override get': function( key )
    {
        return this.__super( key )
            .then( val => val + ' get' );
    },
} );


describe( 'store.MissLookup', () =>
{
    it( 'requires function for cache miss', () =>
    {
        expect( () => StubStore.use( Sut( {} ) )() )
            .to.throw( TypeError );
    } );

    it( 'invokes lookup on cache miss', () =>
    {
        const expected = 'quux';
        const miss     = ( key ) => Promise.resolve( key + expected );
        const sut      = StubStore.use( Sut( miss ) )();

        // key + expected + StubStore#get
        return Promise.all( [
            expect( sut.get( 'foo' ) )
                .to.eventually.equal( 'foo' + expected + ' get' ),

            expect( sut.get( 'bar' ) )
                .to.eventually.equal( 'bar' + expected + ' get' ),
        ] );
    } );


    it( 'caches miss lookup', () =>
    {
        let calln = 0;

        const expected = {};

        function miss()
        {
            // should not be called more than once
            expect( ++calln ).to.equal( 1 );
            return Promise.resolve( expected );
        }

        const sut = Store.use( Sut( miss ) )();

        // should miss
        return expect( sut.get( 'foo' ) ).to.eventually.equal( expected )
            .then( () =>
            {
                // should not miss
                expect( sut.get( 'foo' ) ).to.eventually.equal( expected );
            } );
    } );


    it( 'does not miss on existing cache item', () =>
    {
        const fail = () => { throw Error( 'Should not have missed' ) };
        const sut  = Store.use( Sut( fail ) )();

        return expect(
            sut.add( 'foo', 'bar' )
                .then( () => sut.get( 'foo' ) )
        ).to.eventually.equal( 'bar' );
    } );


    // prevent stampeding and concurrency issues
    it( 'shares promise given concurrent miss requests', () =>
    {
        let n       = 0;
        let resolve = null;

        const p = new Promise( r => resolve = r );

        // return our mock promise, which should only be once (after
        // that, the SUT should have cached the promise)
        function miss()
        {
            if ( n++ > 0 ) throw Error( 'Miss called more than once' );
            return p;
        }

        const sut = Store.use( Sut( miss ) )();

        // set of three promises, each on the same key
        const misses = [ 1, 2, 3 ].map( i => sut.get( 'foo' ) );

        // we don't really care what promises were returned to us
        // (that's an implementation detail), but we do care that they
        // all resolve once we resolve our promise
        resolve( true );

        return Promise.all( misses );
    } );


    it( 'does not share old promise after miss resolves', () =>
    {
        let missret = {};

        const key   = 'foo';
        const miss1 = {};
        const miss2 = {};

        function miss()
        {
            return Promise.resolve( missret );
        }

        const sut = Store.use( Sut( miss ) )();

        missret = miss1;

        return sut.get( key )
            .then( val => expect( val ).to.equal( miss1 ) )
            .then( () =>
            {
                sut.clear();

                missret = miss2;
                return sut.get( key )
                    .then( val => expect( val ).to.equal( miss2 ) )
            } );
    } );
} );