Expressing Expectations with はず

Adding the word はず to the end of a sentence in the plain form will express a meaning like "I expect that" or "It is supposed to be the case that..." はず is used as a regular noun, and so the standard grammar rules apply there (using の between a noun and はず, using な after a na-adjective).

明日は天気がいいはずです。
The weather is supposed to be good tomorrow.

リーさんの料理は美味しいはずよ。
Lee-san's cooking is supposed to be delicious.

These sentences show things that you expect to be true based on common sense or other notions that naturally lead to such a belief. For example, perhaps I heard that Lee has taken several cooking classes, and thus I expect his cooking to be good.

はず can't be used to express things that a person is "supposed" to do because of responsibility or duty. We wouldn't want to use it to say "You're supposed to teach your kids to eat healthy" because that more refers to a parents' duty.

Since はず is a normal noun, it can also be conjugated to past tense with だった or でした to express something that was supposed to have been the case, but actually turned out otherwise. When doing this, the part before はず is in the present tense.

パーティーでケーキがあるはずだったけど、なかったよ。
I expected there to be cake at the party, but there wasn't.

アリスと走りに行くはずだったけど、喫茶店に行った。
I was expecting to go on a run with Alice, but we went to a cafe.

Finally, to express something that was not expected, the form はずがない is used. It can also mean that something is inconceivable.

田中先生の試験が易しいはずがない。
Tanaka-sensei's tests aren't supposed to be easy.

かばと公園に行くのが楽しいはずがない。
Going to the park with a hippo isn't supposed to be fun.