It's important to remember that often she is not deliberately testing
you. It's not necessarily something that she is consciously aware of. She
just gets a feeling to behave a certain way, and so she does. Depending
on how you react, she feels either more or less attracted as a result. This
is known as a congruence test.
If she views you as a contender, then she will test you. A woman often
won't even bother to test a low-value male; instead, she will just
become nonresponsive and then leave as soon as possible. Thus a test
can be considered an indicator of interest of sorts.
Congruence tests are a double-edged sword: If you respond the
right way, she will be noticeably more attracted to you after the test.
But if you fail, then she will be noticeably less attracted.