Remove support for legacy jUnit 4 Spock Groovy tests

.run/test.run.xml

@@ -0,0 +1,15 @@
+<component name="ProjectRunConfigurationManager">
+  <configuration default="false" name="test" type="JUnit" factoryName="JUnit">
+    <module name="sirius-kernel" />
+    <option name="PACKAGE_NAME" value="" />
+    <option name="MAIN_CLASS_NAME" value="" />
+    <option name="METHOD_NAME" value="" />
+    <option name="TEST_OBJECT" value="tags" />
+    <option name="VM_PARAMETERS" value="-ea -Dtest.excluded.groups=nightly" />
+    <option name="WORKING_DIRECTORY" value="$MODULE_DIR$" />
+    <tag value="!nightly" />
+    <method v="2">
+      <option name="Make" enabled="true" />
+    </method>
+  </configuration>
+</component>

README.md

@@ -103,9 +103,9 @@ a single test (method) - the tests have to function independently of their surro
 has to either succeed in all three scenarios or it must fail each time. Everything else indicates an invalid test
 setup._
 
+Tests which require a running SIRIUS framework should use [`SiriusExtension`](src/test/java/sirius/kernel/SiriusExtension.java).
+
 For testing, we heavily rely on **Docker** (especially when external systems like databases are required).
 SIRIUS has a build-in helper to start and stop **docker-compose** setups.
 See [DockerHelper](src/main/java/sirius/kernel/DockerHelper.java) for a list of supported configuration
-settings or refer the [test setup](https://github.com/scireum/sirius-db/tree/main/src/test/resources)
-of [sirius-db](https://github.com/scireum/sirius-db) and its
-[TestSuite](https://github.com/scireum/sirius-db/blob/main/src/test/java/TestSuite.java) as an elaborate example.
+settings or refer the [test setup](https://github.com/scireum/sirius-db/tree/main/src/test/resources) of [sirius-db](https://github.com/scireum/sirius-db) as an elaborate example.

pom.xml

@@ -6,7 +6,7 @@
     <parent>
         <groupId>com.scireum</groupId>
         <artifactId>sirius-parent</artifactId>
-        <version>14.3.3</version>
+        <version>15.0.0</version>
     </parent>
     <artifactId>sirius-kernel</artifactId>
     <name>SIRIUS kernel</name>