有一次考试英语

There will be a test after the term begins.

We will have an English test in the Thursday.

在星期四，我们将有一次英语考试。这句话显然是将来时所以英语是We will have a English test on Thursday.

在星期四我们将有一次英语考试。We'll have an English test on Thursday.

a math exam

从学生的角度来说，“参加考试”，两个词都可以，可互换，即have an exam= take an exam = sit an exam (美语，英语则一般表达为sit for an exam). 甚至也可以说“do an exam”，意思都是一样的。从老师的角度来说，举行一次考试可以用 give an exam ，也有人用set an exam (包含“预备、准备”的意思)如：The teacher gave the students an exam.或者: The teacher set an exam for the students.前者更为常用。