Introduce assertj test lib to make the throw exception test more accu… (#10779)

### Summary
This change introduced the assertj test lib to make the throw exception
testing more accurate

### Test plan
./gradlew :executorch_android:testDebugUnitTest

---------

Co-authored-by: Haiting Pu <[email protected]>

Author: phaiting

extension/android/executorch_android/build.gradle

@@ -49,6 +49,7 @@ dependencies {
     implementation 'com.facebook.soloader:nativeloader:0.10.5'
     implementation libs.core.ktx
     testImplementation 'junit:junit:4.12'
+    testImplementation 'org.assertj:assertj-core:3.27.2'
     androidTestImplementation 'androidx.test.ext:junit:1.1.5'
     androidTestImplementation 'androidx.test:rules:1.2.0'
     androidTestImplementation 'commons-io:commons-io:2.4'

extension/android/executorch_android/src/main/java/org/pytorch/executorch/Tensor.java

@@ -394,7 +394,9 @@ public byte[] getDataAsByteArray() {
    */
   public byte[] getDataAsUnsignedByteArray() {
     throw new IllegalStateException(
-        "Tensor of type " + getClass().getSimpleName() + " cannot return data as byte array.");
+        "Tensor of type "
+            + getClass().getSimpleName()
+            + " cannot return data as unsigned byte array.");
   }
 
   /**