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

t.insert( { _id : 1 , a : 2 , b : 3 } );
assert.eq( 1 , t.getIndexes().length , "A1" );

t.ensureIndex( { a : 1 } );
t.ensureIndex( { b : 1 } );
assert.eq( 3 , t.getIndexes().length , "A2" );

x = db._dbCommand( { dropIndexes: t.getName() , index : t._genIndexName( { a : 1 } ) } );
assert.eq( 2 , t.getIndexes().length , "B1" );

x = db._dbCommand( { dropIndexes: t.getName() , index : { b : 1 } } )
assert.eq( 1 , t.getIndexes().length , "B2" );

// ensure you can recreate indexes, even if you don't use dropIndex method
t.ensureIndex({a:1});
assert.eq(2 , t.getIndexes().length);