Android prob with AndroidJUnitRunner giving 'java.lang.ClassNotFoundException'

I am new in Instrumentation testing. I am trying basic testing with AndroidJUnitRunner. Here is my gradle:

apply plugin: 'com.android.application'

android {
    compileSdkVersion 24
    buildToolsVersion "25.0.0"
    defaultConfig {
        applicationId "com.kaushik.mycart.ui"
        minSdkVersion 15
        targetSdkVersion 24
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
        jackOptions.enabled true
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
    compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_8
        targetCompatibility JavaVersion.VERSION_1_8
    }
}

dependencies {
    compile fileTree(dir: 'libs', include: ['*.jar'])
    androidTestCompile('com.android.support.test.espresso:espresso-core:2.2.2', {
        exclude group: 'com.android.support', module: 'support-annotations'
    })

    ..........................
    ..........................

    testCompile 'junit:junit:4.12'
    testCompile 'org.mockito:mockito-core:1.10.19'
    androidTestCompile 'org.hamcrest:hamcrest-library:1.3'

}

Then I added a class named 'ProductListActivityTest' to test with AndroidJunitRunner. It is below:

package com.kaushik.myredmart.ui;
// all includes
@RunWith(AndroidJUnit4.class)
public class ProductListActivityTest {

    @Rule
    public ActivityTestRule<ProductListActivity> rule  = new  ActivityTestRule<>(ProductListActivity.class);

    @Test
    public void ensureListViewIsPresent() throws Exception {
        ProductListActivity activity = rule.getActivity();
        View viewByIdw = activity.findViewById(R.id.productListView);
        assertThat(viewByIdw,notNullValue());
        assertThat(viewByIdw, instanceOf(RecyclerView.class));
        RecyclerView productListView = (RecyclerView) viewByIdw;
        RecyclerView.Adapter adapter = productRecyclerView.getAdapter();
        assertThat(adapter, instanceOf(ProductAdapter.class));

    }
}

I have added no other file in 'androidTest'. I like to also mention that there is Application class file in my source code. Now every time I try to run the test, it is giving following error:

Started running tests
Test running failed: Instrumentation run failed due to 'java.lang.ClassNotFoundException'
Empty test suite.

Can anyone help me identifying the problem in my test code?

I solved the problem. It is due to difference of Package names. I set all package name uniform and run again. It works. Thank you all for helping.