Isolate core unit tests per classloader (#4156)

* Isolate core unit tests per classloader

* Stabilize core unit tests initialization

Author: shai-almog

maven/core-unittests/pom.xml

@@ -33,6 +33,11 @@
                 <groupId>org.apache.maven.plugins</groupId>
                 <artifactId>maven-surefire-plugin</artifactId>
                 <version>3.2.1</version>
+                <configuration>
+                    <!-- Run each test in its own forked JVM to ensure an isolated classloader. -->
+                    <forkCount>1</forkCount>
+                    <reuseForks>false</reuseForks>
+                </configuration>
             </plugin>
             <plugin>
                 <groupId>org.jacoco</groupId>

maven/core-unittests/src/test/java/com/codename1/io/CacheMapTest.java

@@ -1,5 +1,6 @@
 package com.codename1.io;
 
+import com.codename1.impl.ImplementationFactory;
 import com.codename1.junit.EdtTest;
 import com.codename1.testing.TestCodenameOneImplementation;
 import com.codename1.ui.Display;
@@ -17,6 +18,15 @@ class CacheMapTest {
     @BeforeEach
     void setUp() {
         implementation = new TestCodenameOneImplementation(true);
+        ImplementationFactory.setInstance(new ImplementationFactory() {
+            @Override
+            public Object createImplementation() {
+                return implementation;
+            }
+        });
+        if (!Display.isInitialized()) {
+            Display.init(null);
+        }
         Util.setImplementation(implementation);
         Storage.setStorageInstance(null);
     }
@@ -25,6 +35,7 @@ void setUp() {
     void tearDown() {
         Storage.setStorageInstance(null);
         Util.setImplementation(null);
+        Display.deinitialize();
     }
 
     @Test

maven/core-unittests/src/test/java/com/codename1/properties/PropertiesPackageTest.java

@@ -25,7 +25,7 @@ class PropertiesPackageTest extends UITestBase {
 
     @BeforeEach
     void setup() throws Exception {
-        CN.callSeriallyAndWait(new Runnable() {
+        Runnable setupTask = new Runnable() {
             public void run() {
                 originalPreferencesLocation = Preferences.getPreferencesLocation();
                 Preferences.setPreferencesLocation("PropertiesTest-" + System.nanoTime());
@@ -36,12 +36,17 @@ public void run() {
                 PropertyBase.bindGlobalGetListener(null);
                 PropertyBase.bindGlobalSetListener(null);
             }
-        });
+        };
+        if (CN.isEdt()) {
+            setupTask.run();
+        } else {
+            CN.callSeriallyAndWait(setupTask);
+        }
     }
 
     @AfterEach
     void tearDown() throws Exception {
-        CN.callSeriallyAndWait(new Runnable() {
+        Runnable teardownTask = new Runnable() {
             public void run() {
                 PropertyBase.bindGlobalGetListener(null);
                 PropertyBase.bindGlobalSetListener(null);
@@ -52,7 +57,12 @@ public void run() {
                 Storage.getInstance().clearCache();
                 implementation.clearStorage();
             }
-        });
+        };
+        if (CN.isEdt()) {
+            teardownTask.run();
+        } else {
+            CN.callSeriallyAndWait(teardownTask);
+        }
     }
 
     @EdtTest