Prevent Junit 4 tests from being skipped due to jupiter engine (jenkinsci#5713)

* Prevent Junit 4 tests from being skipped due to jupiter engine

@jglick suggested before when this happened we should have a check but I
never implemented it.
now it has happened again lets add the checj to make sure tests do not
get skipped withouth anyone realising because we accidently pull in
jupiter-engine.

* Update core/src/test/java/jenkins/Junit4TestsRanTest.java

Co-authored-by: Mark Waite <mark.earl.waite@gmail.com>

* test case needs to be public!

* the missing tests where from the test package

The tests not being executied due to jenkinsci#5703 where in the test package, so
add a test and check there too.

Co-authored-by: Mark Waite <mark.earl.waite@gmail.com>

Author: jtnord

Jenkinsfile

@@ -60,6 +60,12 @@ for(j = 0; j < jdks.size(); j++) {
                     if (runTests) {
                         junit healthScaleFactor: 20.0, testResults: '*/target/surefire-reports/*.xml,war/junit.xml'
                         archiveArtifacts allowEmptyArchive: true, artifacts: '**/target/surefire-reports/*.dumpstream'
+                        if (! fileExists('core/target/surefire-reports/TEST-jenkins.Junit4TestsRanTest.xml') ) {
+                            error 'junit 4 tests are no longer being run for the core package'
+                        }
+                        if (! fileExists('test/target/surefire-reports/TEST-jenkins.Junit4TestsRanTest.xml') ) {
+                            error 'junit 4 tests are no longer being run for the test package'
+                        } // cli has been migrated to junit 5
                     }
                     if (buildType == 'Linux' && jdk == jdks[0]) {
                         def changelist = readFile(changelistF)

core/src/test/java/jenkins/Junit4TestsRanTest.java

@@ -0,0 +1,13 @@
+package jenkins;
+
+import org.junit.Test;
+
+public class Junit4TestsRanTest {
+
+    @Test
+    public void anything() {
+        // intentionally blank.
+        // we just want a test that runs with junit 4 so that if tests get skipped due to the introduction of jupiter engine we are alerted
+    }
+
+}

test/src/test/java/jenkins/Junit4TestsRanTest.java

@@ -0,0 +1,13 @@
+package jenkins;
+
+import org.junit.Test;
+
+public class Junit4TestsRanTest {
+
+    @Test
+    public void anything() {
+        // intentionally blank.
+        // we just want a test that runs with junit 4 so that if tests get skipped due to the introduction of jupiter engine we are alerted
+    }
+
+}