Slightly modified test from SERVER-10015 (originally written by Greg)

balancer_with_inconsistent_config.js

//
// Tests whether the balancer continues with inconsistent chunks
//

var options = {separateConfig : true, sync : true};

var st = new ShardingTest({shards : 2, mongos : 1, other : options});

st.stopBalancer();

var mongos = st.s;
var shards = mongos.getDB("config").shards.find().toArray();
var lastConfig = st.config2;
var coll = mongos.getCollection("foo.bar");

jsTest.log("Creating sharded connection...");

assert(mongos.adminCommand({enableSharding : coll.getDB() + ""}).ok);
printjson(mongos.adminCommand({movePrimary : coll.getDB() + "", to : shards[0]._id}));
assert(mongos.adminCommand({shardCollection : coll + "", key : {_id : 1}}).ok);

jsTest.log("Splitting first chunks.");

for ( var i = 0; i < 20; i++) {
    assert(mongos.adminCommand({split : coll + "", middle : {_id : i}}).ok);
}

var origChunks = mongos.getDB("config").chunks.find().toArray();

printjson(mongos.getDB("config").chunks.find().toArray());
printjson(lastConfig.getDB("config").chunks.find().toArray());

jsTest.log("Moving chunk and rolling back only last config server.");

assert(mongos.adminCommand({moveChunk : coll + "", find : {_id : 0}, to : shards[1]._id}).ok);
lastConfig.getDB("config").chunks.remove();
for ( var i = 0; i < origChunks.length; i++) {
    lastConfig.getDB("config").chunks.insert(origChunks[i]);
}
assert.eq(null, lastConfig.getDB("config").getLastError());

var moveChunksBefore = mongos.getDB("config").changelog.find({ what: 'moveChunk.start' }).count();

// Wait for config checker to detect inconsistency.
sleep( 120 * 1000 );

// Wait 30 seconds for the balancer to move chunks, if it is going to
st.startBalancer();
sleep( 30 * 1000 );

var moveChunksAfter = mongos.getDB("config").changelog.find({ what: 'moveChunk.start' }).count();

// We should at most have tried to move one chunk with inconsistent data and realized the problem
// TODO: Better to not move at all, but potentially hard to check.
assert.eq(moveChunksBefore, moveChunksAfter);

st.stop();