In the description you say:
"If the grade of a student is equal to the acceptance grade, he will pass the exam."
Could be more precise as students with higher grades should also pass the exam, shouldn'n they?!
You should also add a test for equality of grades.
For now both '>' and '>=' checks pass the tests.

In C# unit test code you could omit the [Test] attribute when using [TestCase] attributes.

Either use bool instead of Boolean return value or add 'using System;'