how to add unit test to java project in intellij IDEA

I want to create simple java project with jUnit, so for example I'm want to write an algorithm like merge sort or some java class and create test class so I can make unit test for that class.

I've create the project with :

File -> New -> Project -> java -> next and setup the project name and location

and I want to make the unit test for the class the I've created, and I've tried the following solotions :

1. solutions 1 from intellij dosc using the light bulb to create the test class
2. solutions 2 using shortcut [ctrl + shift + t]

But I always endup with import static org.junit.Assert.*; cannot resolve symbol 'junit', I tried different unit test library end up the same way.

How to resolve this problem so I can make unit test class in this simple java project?