Ignore sun packages when importing full classpath

resolves #1446

The CI build has recently often failed on `ubuntu` and `macos` with Java 8,
due to `java.lang.OutOfMemoryError: GC overhead limit exceeded`.

This is due to `ClassFileImporterSlowTest` importing the full classpath in some tests,
which gives more than 20k classes on Java 8,
which contains 7k classes in `com.sun` and 4k classes in `sun` packages
that can easily be ignored.

Signed-off-by: Manfred Hanke <Manfred.Hanke@tngtech.com>

Author: hankem

archunit/src/test/java/com/tngtech/archunit/core/importer/ClassFileImporterSlowTest.java

@@ -35,6 +35,13 @@
 
 @Category(Slow.class)
 public class ClassFileImporterSlowTest {
+    /**
+     * Importing the full classpath may give thousands of classes in {@link sun} and (especially for Java 8) {@link com.sun} packages.
+     * Importing those would increase the memory footprint of the test tremendously, but not give an additional benefit for the test,
+     * so they are excluded for convenience.
+     */
+    private static final ImportOption EXCLUDE_SUN_PACKAGES = l -> !l.contains("/sun/");
+
     @Rule
     public final TransientCopyRule copyRule = new TransientCopyRule();
     @Rule
@@ -53,6 +60,7 @@ public void imports_the_classpath_without_archives() {
         assertThatTypes(classes).doNotContain(File.class); // Default does not import JDK classes
 
         classes = new ClassFileImporter()
+                .withImportOption(EXCLUDE_SUN_PACKAGES)
                 .withImportOption(importJavaBaseOrRtAndJUnitJarAndFilesOnTheClasspath())
                 .importClasspath();
 
@@ -73,10 +81,12 @@ public void imports_the_classpath_using_multiple_ImportOptions() {
     @Test
     public void importing_the_default_package_equals_importing_the_classpath() {
         Set<String> classNamesOfDefaultPackageImport = new ClassFileImporter()
+                .withImportOption(EXCLUDE_SUN_PACKAGES)
                 .withImportOption(importJavaBaseOrRtAndJUnitJarAndFilesOnTheClasspath())
                 .importPackages("")
                 .stream().map(JavaClass::getName).collect(toSet());
         Set<String> classNamesOfClasspathImport = new ClassFileImporter()
+                .withImportOption(EXCLUDE_SUN_PACKAGES)
                 .withImportOption(importJavaBaseOrRtAndJUnitJarAndFilesOnTheClasspath())
                 .importClasspath()
                 .stream().map(JavaClass::getName).collect(toSet());
@@ -180,6 +190,7 @@ public void creates_JavaPackages() {
 
     private JavaClasses importJavaBase() {
         return new ClassFileImporter()
+                .withImportOption(EXCLUDE_SUN_PACKAGES)
                 .withImportOption(location ->
                         // before Java 9 packages like java.lang were in rt.jar
                         location.contains("rt.jar") ||