Add Checkstyle rule ensuring Jupiter Assertions are self-contained

Author: marcphilipp

gradle/config/checkstyle/checkstyleMain.xml

@@ -34,6 +34,14 @@
 			<property name="message" value="Please use String.formatted() (non-static) rather than String.format() (static)."/>
 			<property name="ignoreComments" value="true"/>
 		</module>
+		<module name="com.puppycrawl.tools.checkstyle.checks.regexp.RegexpSinglelineJavaCheck">
+			<!-- see https://github.com/junit-team/junit-framework/issues/4604 -->
+			<property name="id" value="jupiterAssertions"/>
+			<property name="maximum" value="0"/>
+			<property name="format" value="org\.junit\.jupiter\.api\.(Assertions|Assumptions)\."/>
+			<property name="message" value="Assertions/Assumptions should not be used in production code."/>
+			<property name="ignoreComments" value="true"/>
+		</module>
 		<module name="HideUtilityClassConstructor"/>
 		<module name="ModifierOrder"/>
 		<module name="EqualsAvoidNull"/>