Java – Eclipse No tests found using JUnit 5 caused by NoClassDefFoundError for LauncherFactory

The problem

Whenever I run my projects JUnit test (using JUnit 5 with Java 9 and Eclipse Oxygen 1.a) I encounter the problem that eclipse can't find any tests.

The description

Under the run configuration, eclipse can't even find the method which is annotated with @Test, but instead only shows me "(all methods)".
The following picture hopefully gives a better glimps of my setup:

Console output:

java.lang.NoClassDefFoundError: org/junit/platform/launcher/core/LauncherFactory
    at org.eclipse.jdt.internal.junit5.runner.JUnit5TestLoader.<init>(JUnit5TestLoader.java:31)
    at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
    at java.base/jdk.internal.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
    at java.base/java.lang.reflect.Constructor.newInstance(Unknown Source)
    at java.base/java.lang.Class.newInstance(Unknown Source)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.createRawTestLoader(RemoteTestRunner.java:368)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.createLoader(RemoteTestRunner.java:363)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.defaultInit(RemoteTestRunner.java:307)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.init(RemoteTestRunner.java:222)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:206)
Caused by: java.lang.ClassNotFoundException: org.junit.platform.launcher.core.LauncherFactory
    at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(Unknown Source)
    at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(Unknown Source)
    at java.base/java.lang.ClassLoader.loadClass(Unknown Source)
    ... 11 more

What I tried so far

I've already tried

• to remove the test folder from build path and add it again.
• to start the test with hovering over the method annotated with @Test and then click "Run as JUnit Test".
• remove JUnit from Buildpath and add it again
• restart eclipse
• I've also moved the project whole project from one machine to another machine and tried it with the provided eclipse installation there
• to rename the test method.
• to retype the @Test annotation

Some of these steps can be found here, but in the end the problem remained.