Expected hat draw to reduce number of items in contents

The READ.md states “The balls should not go back into the hat during the draw, similar to an urn experiment without replacement.” Doesn’t this mean that once the draw is done the contents should remain unchanged?

The test_hat_draw test says “Expected hat draw to reduce number of items in contents.”

If the hat draw reduces the items in the contents doesn’t this make it impossible to run multiple experiments against the contents?

What am I missing?

EDIT - The draw should reduce the contents. The hat object inside the experiment function should be copied at the beginning of each test.

I interpret that to mean that you are taking it out of the hat.

If I have a hat with there are 10 white balls and 10 black balls and I pull one out, and it is a white ball, then there are now 19 balls left: 9 white and 10 black.

It mentions the “urn experiment” which is a common group of problems in probability. In some version, you put the ball back after selecting, and sometimes you don’t. That’s what they mean by “without replacement”, in other words, you are not placing the ball back in the hat/urn, but keeping it out, thereby reducing the number of balls.