Added jstest for http://jira.mongodb.org/browse/SERVER-1896

jstests/sharding/limit_push.js

@@ -0,0 +1,54 @@
+// This test is to ensure that limit() clauses are pushed down to the shards and evaluated
+// See: http://jira.mongodb.org/browse/SERVER-1896
+
+doTest = function( ) {
+
+	s = new ShardingTest( "limit_push", 2, 1, 1 );
+
+	db = s.getDB( "test" );
+
+	// Create some data
+	for (i=0; i < 100; i++) { db.limit_push.insert({ _id : i, x: i}); } 
+	db.limit_push.ensureIndex( { x : 1 } );
+	assert.eq( 100 , db.limit_push.find().length() , "Incorrect number of documents" );
+
+	// Shard the collection
+	s.adminCommand( { enablesharding : "test" } );
+	s.adminCommand( { shardcollection : "test.limit_push" , key : { x : 1 } } );
+
+	// Now split the and move the data between the shards
+	s.adminCommand( { split : "test.limit_push", middle : { x : 50 }} ); 
+	s.adminCommand( { moveChunk: "test.limit_push", find : { x : 51}, to : "shard0000" }) 
+
+	// Check that the chunck have split correctly
+	assert.eq( 2 , s.config.chunks.count() , "wrong number of chunks");
+
+	// The query is asking for the maximum value below a given value
+	// db.limit_push.find( { x : { $lt : 60} } ).sort( { x:-1} ).limit(1)
+	q = { x : { $lt : 60} }; 
+
+	// Make sure the basic queries are correct
+	assert.eq( 60 , db.limit_push.find( q ).count() , "Did not find 60 documents" );
+	//rs = db.limit_push.find( q ).sort( { x:-1} ).limit(1)
+	//assert.eq( rs , { _id : "1" , x : 59 } , "Did not find document with value 59" );
+
+	// Now make sure that the explain shos that each shard is returning a single document as indicated
+	// by the "n" element for each shard
+	exp = db.limit_push.find( q ).sort( { x:-1} ).limit(1).explain();
+
+	assert.eq("ParallelSort", exp.clusteredType, "Not a ParallelSort");
+
+	var k = 0;
+	for (var j in exp.shards) {
+		assert.eq( 1 , exp.shards[j][0].n, "'n' is not 1 from shard000" + k.toString());
+		k++
+	}
+
+	s.stop();
+
+}
+
+// Uncomment this when the bug is fixed
+// doTest();
+
+