[SUREFIRE-2210] - Restore ordering of additional class path elements

maven-surefire-common/src/main/java/org/apache/maven/plugin/surefire/AbstractSurefireMojo.java

@@ -2569,7 +2569,7 @@ private TestClassPath generateTestClasspath() throws MojoFailureException {
 
         Map<String, Artifact> dependencyConflictIdsProjectArtifacts = classpathArtifacts.stream()
                 .collect(Collectors.toMap(Artifact::getDependencyConflictId, Function.identity()));
-        Set<String> additionalClasspathElements = new HashSet<>();
+        Set<String> additionalClasspathElements = new LinkedHashSet<>();
         if (getAdditionalClasspathElements() != null) {
             Arrays.stream(getAdditionalClasspathElements()).forEach(additionalClasspathElements::add);
         }

surefire-its/src/test/resources/additional-classpath/extraResource/order-test.txt

@@ -0,0 +1 @@
+1

surefire-its/src/test/resources/additional-classpath/extraResource2/order-test.txt

@@ -0,0 +1 @@
+2

surefire-its/src/test/resources/additional-classpath/src/test/java/additionalClasspath/BasicTest.java

@@ -1,5 +1,12 @@
 package additionalClasspath;
 
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.InputStreamReader;
+import java.net.URL;
+import java.util.Enumeration;
+
 import junit.framework.TestCase;
 
 public class BasicTest
@@ -12,4 +19,23 @@ public void testExtraResource()
         assertNotNull( BasicTest.class.getResourceAsStream( "/test2.txt" ) );
     }
 
+    public void testExtraResourceOrder() throws IOException
+    {
+        Enumeration<URL> resources = BasicTest.class.getClassLoader().getResources("/order-test.txt");
+        assertTrue( resources.hasMoreElements() );
+        URL url = resources.nextElement();
+        InputStream is = url.openStream();
+        assertNotNull( is );
+        try ( InputStream i = is; InputStreamReader r = new InputStreamReader(is); BufferedReader br = new BufferedReader(r) ) {
+            assertEquals("1", br.readLine());
+        }
+        assertTrue( resources.hasMoreElements() );
+        url = resources.nextElement();
+        is = url.openStream();
+        assertNotNull( is );
+        try ( InputStream i = is; InputStreamReader r = new InputStreamReader(is); BufferedReader br = new BufferedReader(r) ) {
+            assertEquals("2", br.readLine());
+        }
+        assertFalse( resources.hasMoreElements() );
+    }
 }