If you are going to use this annotation, you must import junit.jar or tesng.jar
In this situation, i suggest you to select tesng instead of junit to run your tests.
Create a maven project in Eclipse and add below dependencies on pom.xml
<dependency>
<groupId>org.seleniumhq.selenium</groupId>
<artifactId>selenium-java</artifactId>
<version>LATEST</version>
</dependency>
<dependency>
<groupId>org.testng</groupId>
<artifactId>testng</artifactId>
<version>6.9.6</version>
</dependency>
If you are going to test mobile, then you need to add appium as well.
<dependency>
<groupId>io.appium</groupId>
<artifactId>java-client</artifactId>
<version>3.2.0</version>
</dependency>
Then you can use @Test annotation in your tests.