Why am I getting NoClassDefFoundError even after having the class in testing in Android Studio

Question

I'm trying to test my Helper class which is a Kotlin class in Android Studio. I've JUnit dependencies as it is that I get with new Project creation. But, whenever I try to run test, I get NoClassDefFoundError. I'm also not able to generate tests of Junit using right click menu because there is no such option there.

dependency:

Build.gradle(app)
testImplementation(libs.junit)

libs.versions.toml: 
junit = { group = "junit", name = "junit", version.ref = "junit" }

Helper class:

package com.shivanshu.test.utils

class Helper {

    fun isPalindrome(input: String): Boolean {
        var i = 0
        var j = input.length - 1
        var result = true
        while (i < j) {
            if (input[i] != input[j]) {
                result = false
            }
            i++
            j--
        }
        return result
    }

}

Helper test:

package com.shivanshu.test.utils

import junit.framework.TestCase.assertEquals
import org.junit.Test

class HelperTest {
    @Test
    fun isPalindrome(){
        val helper = Helper()
        val result=helper.isPalindrome("hello")
        assertEquals(true, result)
    }
}

Error:

java.lang.NoClassDefFoundError: com/shivanshu/test/utils/Helper

    at com.shivanshu.test.utils.HelperTest.isPalindrome(HelperTest.kt:9)
    at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(Unknown Source)
    at java.base/java.lang.reflect.Method.invoke(Unknown Source)
    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:45)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:15)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:42)
    at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:20)
    at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:263)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:68)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:47)
    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:231)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:60)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:229)
    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:50)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:222)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:300)
    at org.junit.runner.JUnitCore.run(JUnitCore.java:157)
    at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:69)
    at com.intellij.rt.junit.IdeaTestRunner$Repeater$1.execute(IdeaTestRunner.java:38)
    at com.intellij.rt.execution.junit.TestsRepeater.repeat(TestsRepeater.java:11)
    at com.intellij.rt.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:35)
    at com.intellij.rt.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:232)
    at com.intellij.rt.junit.JUnitStarter.main(JUnitStarter.java:55)
Caused by: java.lang.ClassNotFoundException: com.shivanshu.test.utils.Helper
    at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(Unknown Source)
    at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(Unknown Source)
    at java.base/java.lang.ClassLoader.loadClass(Unknown Source)
    ... 23 more

I tried checking JUnit version. Running Gradle test works fine. I also am not able to generate test in my Kotlin based Android Studio Ladybug. I just don't get option to generate Test in generate options in right click menu. I also tried configuring test related code in build.gradle. But nothing worked. I tried mimicking package structure also.