Introduce FULL_JDK_15 TestJdkKind

compiler/tests-common/tests/org/jetbrains/kotlin/test/KotlinTestUtils.java

@@ -365,6 +365,9 @@ public class KotlinTestUtils {
         else if (jdkKind == TestJdkKind.FULL_JDK_9) {
             configuration.put(JVMConfigurationKeys.JDK_HOME, getJdk9Home());
         }
+        else if (jdkKind == TestJdkKind.FULL_JDK_15) {
+            configuration.put(JVMConfigurationKeys.JDK_HOME, getJdk15Home());
+        }
         else if (SystemInfo.IS_AT_LEAST_JAVA9) {
             configuration.put(JVMConfigurationKeys.JDK_HOME, new File(System.getProperty("java.home")));
         }
@@ -408,6 +411,15 @@ public class KotlinTestUtils {
         return new File(jdk11);
     }
 
+    @NotNull
+    public static File getJdk15Home() {
+        String jdk15 = System.getenv("JDK_15");
+        if (jdk15 == null) {
+            throw new AssertionError("Environment variable JDK_15 is not set!");
+        }
+        return new File(jdk15);
+    }
+
     public static void resolveAllKotlinFiles(KotlinCoreEnvironment environment) throws IOException {
         List<KotlinSourceRoot> roots = ContentRootsKt.getKotlinSourceRoots(environment.getConfiguration());
         if (roots.isEmpty()) return;
@@ -669,7 +681,7 @@ public class KotlinTestUtils {
 
     public static boolean compileJavaFilesExternallyWithJava9(@NotNull Collection<File> files, @NotNull List<String> options) {
         List<String> command = new ArrayList<>();
-        command.add(new File(getJdk9Home(), "bin/javac").getPath());
+        command.add(new File(jdkHome, "bin/javac").getPath());
         command.addAll(options);
         for (File file : files) {
             command.add(file.getPath());

compiler/tests-common/tests/org/jetbrains/kotlin/test/TestJdkKind.java

@@ -26,6 +26,8 @@ public enum TestJdkKind {
     FULL_JDK_6,
     // JDK found at $JDK_19
     FULL_JDK_9,
+    // JDK found at $JDK_15
+    FULL_JDK_15,
     // JDK found at java.home
     FULL_JDK,
     ANDROID_API,