The correct use of the word 'must' is simply to add an imperative to a suggested action. To refer to something as a 'must - do' is common, but it might be necessary how it became so, because it is colloquial, and a result of shortening of speech. Originally it would have been 'there are several places you must visit when you go to France; you must visit the louvre, and you must visit the Eiffel tower...' this is long winded. To shorten this, we say 'the Eiffel router is a must-see, as is the Louvre'. Grammatically, it is incorrect, but it works because it implies a hypothetical argument as to why one must do this.

You should have written your question like this. Today I saw somebody using "must be" as following: Love's nothing but it must be joyful. To pass your examination, translation test is must . "Must" is model verb as well as noun. The way you have used it as model verb and as noun are both correct.

must- comb. form （must + verb的组合形式） used to form adjectives and nouns denoting things that are essential or highly recommended: a must-visit destination （必须得去的地方） the new material on this disc makes it a must-buy. （这张碟必须得买） 翻译成中文是“必须得” Loves nothing but is must be joyful. 要爱，就必须得爱能够给你带来快乐的东西。 To pass your examination, translation test is must be.  要想顺利通过考试，就必须得搞定翻译测试。