t = db.regex3;
t.drop();

t.save( { name : "eliot" } );
t.save( { name : "emily" } );
t.save( { name : "bob" } );
t.save( { name : "aaron" } );

assert.eq( 2 , t.find( { name : /^e.*/ } ).itcount() , "no index count" );
assert.eq( 4 , t.find( { name : /^e.*/ } ).explain(true).executionStats.totalDocsExamined ,
           "no index explain" );
t.ensureIndex( { name : 1 } );
assert.eq( 2 , t.find( { name : /^e.*/ } ).itcount() , "index count" );
assert.eq( 2 , t.find( { name : /^e.*/ } ).explain(true).executionStats.totalKeysExamined ,
           "index explain" ); // SERVER-239

t.drop();

t.save( { name : "aa" } );
t.save( { name : "ab" } );
t.save( { name : "ac" } );
t.save( { name : "c" } );

assert.eq( 3 , t.find( { name : /^aa*/ } ).itcount() , "B ni" );
t.ensureIndex( { name : 1 } );
assert.eq( 3 , t.find( { name : /^aa*/ } ).itcount() , "B i 1" );
assert.eq( 4 , t.find( { name : /^aa*/ } ).explain(true).executionStats.totalKeysExamined ,
           "B i 1 e" );

assert.eq( 2 , t.find( { name : /^a[ab]/ } ).itcount() , "B i 2" );
assert.eq( 2 , t.find( { name : /^a[bc]/ } ).itcount() , "B i 3" );

t.drop();

t.save( { name: "" } );
assert.eq( 1, t.find( { name: /^a?/ } ).itcount() , "C 1" );
t.ensureIndex( { name: 1 } );
assert.eq( 1, t.find( { name: /^a?/ } ).itcount(), "C 2");