Fixes mockito#2905 : ThreadLocal classes can be mocked.

src/main/java/org/mockito/internal/creation/bytebuddy/MockMethodAdvice.java

@@ -168,7 +168,7 @@ public boolean isMock(Object instance) {
 
     @Override
     public boolean isMocked(Object instance) {
-        return selfCallInfo.checkSelfCall(instance) && isMock(instance);
+        return isMock(instance) && selfCallInfo.checkSelfCall(instance);
     }
 
     @Override

src/test/java/org/mockitousage/bugs/ThreadLocalTest.java

@@ -0,0 +1,60 @@
+/*
+ * Copyright (c) 2007 Mockito contributors
+ * This program is made available under the terms of the MIT License.
+ */
+package org.mockitousage.bugs;
+
+import static org.mockito.Mockito.RETURNS_MOCKS;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.spy;
+
+import org.assertj.core.api.Assertions;
+import org.junit.Test;
+import org.mockito.Mock;
+import org.mockito.MockitoAnnotations;
+import org.mockitoutil.TestBase;
+
+/**
+ * This was an issue reported in #2905. Mocking {@link ThreadLocal} or classes extending {@link ThreadLocal} was
+ * throwing a {@link StackOverflowError}.
+ */
+public class ThreadLocalTest extends TestBase {
+
+    @Test
+    public void mock_ThreadLocal_does_not_raise_StackOverflowError() {
+        StackOverflowError stackOverflowError = Assertions.catchThrowableOfType(() -> {
+            mock(ThreadLocal.class, RETURNS_MOCKS);
+        }, StackOverflowError.class);
+        Assertions.assertThat(stackOverflowError).isNull();
+    }
+
+    @Test
+    public void mock_class_extending_ThreadLocal_does_not_raise_StackOverflowError() {
+        StackOverflowError stackOverflowError = Assertions.catchThrowableOfType(() -> {
+            mock(SomeThreadLocal.class, RETURNS_MOCKS);
+        }, StackOverflowError.class);
+        Assertions.assertThat(stackOverflowError).isNull();
+    }
+
+    @Test
+    public void spy_ThreadLocal_does_not_raise_StackOverflowError() {
+        StackOverflowError stackOverflowError = Assertions.catchThrowableOfType(() -> {
+            spy(ThreadLocal.class);
+        }, StackOverflowError.class);
+        Assertions.assertThat(stackOverflowError).isNull();
+    }
+
+    @Test
+    public void spy_class_extending_ThreadLocal_does_not_raise_StackOverflowError() {
+        StackOverflowError stackOverflowError = Assertions.catchThrowableOfType(() -> {
+            spy(SomeThreadLocal.class);
+        }, StackOverflowError.class);
+        Assertions.assertThat(stackOverflowError).isNull();
+    }
+
+    static class SomeThreadLocal<T> extends ThreadLocal<T> {
+
+    }
+
+}
+