Running all jUnit tests in package with IntelliJ

To run all jUnit tests in a package using IntelliJ click on Run > Edit configurations:

On the left bar, click on the + sign and select JUnit (you must have JUnit plugin and JUnit dependencies on your project).

This will open a Dialog Window to edit the run configuration for a new test.

Name the new configuration, I've used the label <Run all tests>
The fork mode for JUnit allows you to run each test method or class in a separate process, if you're not sure what to use just leave it at <None>. 
On the <Test Kind> field, select the <All in package> option.
On the <Package> field, select the package from where tests should be executed, then click <Ok>.

It is also a good idea to click on the Code Coverage tab and add your test package to run coverage:

Now run your tests by clicking on the shortcut located on the top bar:

 

Results should be displayed at the bottom of the screen:

In case you want to see coverage, use the shortcut:

 

Results displayed on the dialog: