Security Exception When Running Appium Tests with Espresso/Java

I am having an issue setting up Appium to run against an android app. I'm very new to Appium and am trying to implement some UI level automation in a separate java project. I keep hitting the following issue in the appium logs -

[debug] [W3C] Encountered internal error running command: Error: java.lang.SecurityException: Permission Denial: starting instrumentation ComponentInfo{io.appium.espressoserver.test/android.support.test.runner.AndroidJUnitRunner} from pid=7941, uid=7941 not allowed because package io.appium.espressoserver.test does not have a signature matching the target ***

I assume there is a signature discrepancy between the appium project and the app in test, but not sure where to start in resolving this.

The gradle build of my test project -

plugins {
    id 'java'
}

group '***'
version '1.0-SNAPSHOT'

sourceCompatibility = 1.8

repositories {
    mavenCentral()
}

dependencies {
    implementation fileTree(dir: 'libs', include: ['*.jar'])
    testCompile group: 'junit', name: 'junit', version: '4.12'
    compile group: 'com.android.support.test.espresso', name: 'espresso-core', version: '3.1.0'
    compile group: 'io.appium', name: 'java-client', version: '6.1.0'
    compile group: 'org.seleniumhq.selenium', name: 'selenium-java', version: '3.14.0'
}

Note:

• I am using an emulator as I am not able to use a physical device

Thanks in advance for any help and I can provide more info if required (first time actually posting a question here so apologies)