mongo/jstests/core/update_arraymatch7.js

// Check that the positional operator works properly when an index only match is used for the update
// query spec.  SERVER-5067

t = db.jstests_update_arraymatch7;
t.drop();

function testPositionalInc() {
    t.remove({});
    t.save({a: [{b: 'match', count: 0}]});
    t.update({'a.b': 'match'}, {$inc: {'a.$.count': 1}});
    // Check that the positional $inc succeeded.
    assert(t.findOne({'a.count': 1}));
}

testPositionalInc();

// Now check with a non multikey index.
t.ensureIndex({'a.b': 1});
testPositionalInc();