mongo/jstests/datasize.js

f = db.jstests_datasize;
f.drop();

assert.eq( 0, db.runCommand( {datasize:"test.jstests_datasize"} ).size );
f.save( {qq:'c'} );
assert.eq( 32, db.runCommand( {datasize:"test.jstests_datasize"} ).size );
f.save( {qq:'fg'} );
assert.eq( 68, db.runCommand( {datasize:"test.jstests_datasize"} ).size );

f.drop();
f.ensureIndex( {qq:1} );
assert.eq( 0, db.runCommand( {datasize:"test.jstests_datasize"} ).size );
f.save( {qq:'c'} );
assert.eq( 32, db.runCommand( {datasize:"test.jstests_datasize"} ).size );
f.save( {qq:'fg'} );
assert.eq( 68, db.runCommand( {datasize:"test.jstests_datasize"} ).size );

assert.eq( 0, db.runCommand( {datasize:"test.jstests_datasize", min:{qq:'a'}} ).ok );

assert.eq( 68, db.runCommand( {datasize:"test.jstests_datasize", min:{qq:'a'}, max:{qq:'z' }} ).size );
assert.eq( 32, db.runCommand( {datasize:"test.jstests_datasize", min:{qq:'a'}, max:{qq:'d' }} ).size );
assert.eq( 32, db.runCommand( {datasize:"test.jstests_datasize", min:{qq:'a'}, max:{qq:'d' }, keyPattern:{qq:1}} ).size );
assert.eq( 36, db.runCommand( {datasize:"test.jstests_datasize", min:{qq:'d'}, max:{qq:'z' }, keyPattern:{qq:1}} ).size );

assert.eq( 0, db.runCommand( {datasize:"test.jstests_datasize", min:{qq:'c'}, max:{qq:'c' }} ).size );
assert.eq( 32, db.runCommand( {datasize:"test.jstests_datasize", min:{qq:'c'}, max:{qq:'d' }} ).size );

assert.eq( 0, db.runCommand( {datasize:"test.jstests_datasize", min:{qq:'a'}, max:{qq:'d' }, keyPattern:{a:1}} ).ok );