[Java.Interop-Tests] Fix JniTypeTest.Name() missing argument (#538)

Context: dotnet/android#3393

When running the `JniTypeTest.Name()` unit test within Xamarin.Android,
sometimes the unit test runner process would crash.  The crash is
*more* likely in Release runtimes:

	F o.Android_Test: java_vm_ext.cc:570] JNI DETECTED ERROR IN APPLICATION: use of invalid jobject 0xc58fa798
	F o.Android_Test: java_vm_ext.cc:570]     from void crc64f295cabbf85394f5.TestSuiteInstrumentation.n_onStart()
	F o.Android_Test: runtime.cc:630] Runtime aborting...

What was particularly odd about this crash was that after enabling
both GREF and LREF logging, there was no handle 0xc58fa798!

Where was this invalid handle coming from?

Turns Out™, 0xc58fa798 isn't a handle.  Instead, it's a parameter
mismatch!

Commit 9f380eb had a bug.  `JniTypeTest.Name()` was *attempting* to do:

	// Java
	java.lang.reflect.Method Object_hashCode  = Object.class.getMethod("hashCode", new Class[0]);
	String Object_hashCode_returnType         = Object_hashCode.getReturnType();

However, via JNI, it was *actually* doing:

	java.lang.reflect.Method Object_hashCode  = Object.class.getMethod("hashCode", GARBAGE_VALUE);
	String Object_hashCode_returnType         = Object_hashCode.getReturnType();

because it was only passing *one* value to `Class.getMethod()`, not
two values, so the second parameter was entirely undefined and
unknowable.

Through sheer luck (or a terrible bug) this "worked" on a Desktop JVM
and (frequently) in Debug configuration builds of the
`Mono.Android_Tests-*.apk` test app in Xamarin.Android.

On Android in a Release configuration, GARBAGE_VALUE was treated as a
garbage value, and brought down the process because there *was*, in
fact, a JNI error in the application.

Fix `JniTypeTest.Name()`, and pass the correct number of parameters to
`Class.getMethod(String, Class[])`.

Additionally, make two (mostly unrelated) changes:

  * Add a `JniType.ToString()` override.
  * Change the exception ordering in `JavaExceptionTests.StackTrace().

While debugging the above crash, I attempted to use
`JniType.ToString()` in some debug messages.  These were useless,
because there was no `JniType.ToString()` override.

Add one.

The conceptual problem `JavaExceptionTests.StackTrace()`, meanwhile,
is that *eventually* `Java.Lang.Throwable` will be updated to inherit
from `Java.Interop.JavaException`.  If `JavaException` is caught
first, then the `__ANDROID__`-specific behavior around
`Java.Lang.Throwable` will no longer be tested, *and* the test will
continue to pass (while testing subtly different behavior).  Reorder
the `catch` blocks so that when the `Java.Lang.Throwable` base class
changes, the semantics of the test will be unaltered.

Author: jonpryor

src/Java.Interop/Java.Interop/JniType.cs

@@ -57,6 +57,11 @@ public string Name {
 			}
 		}
 
+		public override string ToString ()
+		{
+			return $"JniType(Name='{Name}' PeerReference={PeerReference})";
+		}
+
 #if XA_INTEGRATION
 		internal
 #else   // !XA_INTEGRATION

tests/Java.Interop-Tests/Java.Interop/JavaExceptionTests.cs

@@ -14,28 +14,30 @@ public void StackTrace ()
 		{
 			try {
 				new JniType ("this/type/had/better/not/exist");
-			} catch (JavaException e) {
+			}
+#if __ANDROID__
+			catch (Java.Lang.Throwable e) {
 				Assert.IsTrue (
 						string.Equals ("this/type/had/better/not/exist", e.Message, StringComparison.OrdinalIgnoreCase) ||
 						e.Message.StartsWith ("Didn't find class \"this.type.had.better.not.exist\" on path: DexPathList"));
 				Assert.IsTrue (
 						// ART
-						e.JavaStackTrace.StartsWith ("java.lang.ClassNotFoundException: ", StringComparison.Ordinal) ||
+						e.StackTrace.Contains ("java.lang.ClassNotFoundException: ", StringComparison.Ordinal) ||
 						// Dalvik, JVM
-						e.JavaStackTrace.StartsWith ("java.lang.NoClassDefFoundError: this/type/had/better/not/exist", StringComparison.Ordinal));
+						e.StackTrace.Contains ("java.lang.NoClassDefFoundError: this/type/had/better/not/exist", StringComparison.Ordinal));
 				e.Dispose ();
-#if __ANDROID__
-			} catch (Java.Lang.Throwable e) {
+			}
+#endif  // __ANDROID__
+			catch (JavaException e) {
 				Assert.IsTrue (
 						string.Equals ("this/type/had/better/not/exist", e.Message, StringComparison.OrdinalIgnoreCase) ||
 						e.Message.StartsWith ("Didn't find class \"this.type.had.better.not.exist\" on path: DexPathList"));
 				Assert.IsTrue (
 						// ART
-						e.StackTrace.Contains ("java.lang.ClassNotFoundException: ", StringComparison.Ordinal) ||
+						e.JavaStackTrace.StartsWith ("java.lang.ClassNotFoundException: ", StringComparison.Ordinal) ||
 						// Dalvik, JVM
-						e.StackTrace.Contains ("java.lang.NoClassDefFoundError: this/type/had/better/not/exist", StringComparison.Ordinal));
+						e.JavaStackTrace.StartsWith ("java.lang.NoClassDefFoundError: this/type/had/better/not/exist", StringComparison.Ordinal));
 				e.Dispose ();
-#endif  // __ANDROID__
 			}
 		}
 

tests/Java.Interop-Tests/Java.Interop/JniTypeTest.cs

@@ -141,9 +141,11 @@ public unsafe void Name ()
 				var Class_getMethod         = Class_class.GetInstanceMethod ("getMethod", "(Ljava/lang/String;[Ljava/lang/Class;)Ljava/lang/reflect/Method;");
 				var Method_getReturnType    = Method_class.GetInstanceMethod ("getReturnType", "()Ljava/lang/Class;");
 				var hashCode_str            = JniEnvironment.Strings.NewString ("hashCode");
-				var hashCode_args           = stackalloc JniArgumentValue [1];
-				hashCode_args [0]           = new JniArgumentValue (hashCode_str);
-				var Object_hashCode         = JniEnvironment.InstanceMethods.CallObjectMethod (Object_class.PeerReference, Class_getMethod, hashCode_args);
+				var emptyArray              = JniEnvironment.Arrays.NewObjectArray (0, Class_class.PeerReference, new JniObjectReference ());
+				var getHashcodeMethodArgs   = stackalloc JniArgumentValue [2];
+				getHashcodeMethodArgs [0]   = new JniArgumentValue (hashCode_str);
+				getHashcodeMethodArgs [1]   = new JniArgumentValue (emptyArray);
+				var Object_hashCode         = JniEnvironment.InstanceMethods.CallObjectMethod (Object_class.PeerReference, Class_getMethod, getHashcodeMethodArgs);
 				var Object_hashCode_rt      = JniEnvironment.InstanceMethods.CallObjectMethod (Object_hashCode, Method_getReturnType);
 				try {
 					Assert.AreEqual ("java/lang/Object", Object_class.Name);
@@ -154,6 +156,7 @@ public unsafe void Name ()
 					JniObjectReference.Dispose (ref hashCode_str);
 					JniObjectReference.Dispose (ref Object_hashCode);
 					JniObjectReference.Dispose (ref Object_hashCode_rt);
+					JniObjectReference.Dispose (ref emptyArray);
 				}
 			}
 		}