Fix implementation of proxy mock maker for toString and add additional unit tests.

src/main/java/org/mockito/internal/creation/proxy/ProxyMockMaker.java

@@ -107,7 +107,7 @@ public Object invoke(Object proxy, Method method, Object[] args) throws Throwabl
                     case "equals":
                         return proxy == args[0];
                     case "toString":
-                        return "";
+                        break;
                     default:
                         throw new MockitoException(
                                 join(

src/test/java/org/mockito/internal/creation/proxy/ProxyMockMakerTest.java

@@ -8,6 +8,7 @@
 import org.mockito.internal.creation.AbstractMockMakerTest;
 
 import java.io.Serializable;
+import java.lang.reflect.InvocationHandler;
 import java.lang.reflect.Proxy;
 
 import static org.assertj.core.api.Assertions.assertThat;
@@ -47,5 +48,54 @@ public void should_discover_mockable_input() {
         assertThat(mockMaker.isTypeMockable(SomeInterface.class).mockable()).isTrue();
     }
 
+    @Test
+    public void can_compute_hash_code() throws Throwable {
+        SomeInterface proxy =
+                mockMaker.createMock(settingsFor(SomeInterface.class), dummyHandler());
+
+        InvocationHandler handler = Proxy.getInvocationHandler(proxy);
+
+        assertThat(handler.invoke(proxy, Object.class.getMethod("hashCode"), new Object[0]))
+                .isEqualTo(System.identityHashCode(proxy));
+    }
+
+    @Test
+    public void can_compute_equality() throws Throwable {
+        SomeInterface proxy =
+                mockMaker.createMock(settingsFor(SomeInterface.class), dummyHandler());
+
+        InvocationHandler handler = Proxy.getInvocationHandler(proxy);
+
+        assertThat(
+                        handler.invoke(
+                                proxy,
+                                Object.class.getMethod("equals", Object.class),
+                                new Object[] {proxy}))
+                .isEqualTo(true);
+        assertThat(
+                        handler.invoke(
+                                proxy,
+                                Object.class.getMethod("equals", Object.class),
+                                new Object[] {null}))
+                .isEqualTo(false);
+        assertThat(
+                        handler.invoke(
+                                proxy,
+                                Object.class.getMethod("equals", Object.class),
+                                new Object[] {new Object()}))
+                .isEqualTo(false);
+    }
+
+    @Test
+    public void can_invoke_toString() throws Throwable {
+        SomeInterface proxy =
+                mockMaker.createMock(settingsFor(SomeInterface.class), dummyHandler());
+
+        InvocationHandler handler = Proxy.getInvocationHandler(proxy);
+
+        assertThat(handler.invoke(proxy, Object.class.getMethod("toString"), new Object[0]))
+                .isNull();
+    }
+
     interface SomeInterface {}
 }

subprojects/kotlinTest/src/test/kotlin/org/mockito/kotlin/SuspendTest.kt

@@ -5,8 +5,8 @@
 package org.mockito.kotlin
 
 import kotlinx.coroutines.runBlocking
+import org.hamcrest.MatcherAssert.assertThat
 import org.hamcrest.core.IsEqual
-import org.junit.Assert.assertThat
 import org.junit.Test
 import org.mockito.Mockito.*