Find the Rotation Count in Array

package org.wesome.dsalgo;

public class RotationCount {
    public static int rotationCount(int[] arr, int start, int end) {
        if (start > end) {
            return -1;
        }
        if (start == end) {
            return -1;
        }

        int mid = (start + end) / 2;

//it's not an end and the mid element is greater than its next.
        if (end > mid && arr[mid] > arr[mid + 1])
            return (mid + 1);

//it's not start and the previous element is greater than mid.
        if (mid > start && arr[mid - 1] > arr[mid])
            return mid;

//        if the end is greater than mid means it's sorted, rotation is on the left side.
        if (arr[end] > arr[mid])
            return rotationCount(arr, start, mid - 1);

//        else rotation is in right side.
        return rotationCount(arr, mid + 1, end);
    }
}

package org.wesome.dsalgo;

import org.junit.jupiter.api.Assertions;
import org.junit.jupiter.api.Test;

import static org.wesome.dsalgo.RotationCount.rotationCount;


public class RotationCountTest {

    @Test
    void rotationCountTest1() {
        int[] arr = new int[]{15, 18, 2, 3, 6, 12};
        int rotationCount = rotationCount(arr, 0, arr.length - 1);
        Assertions.assertEquals(2, rotationCount);
    }

    @Test
    void rotationCountTest2() {
        int[] arr = new int[]{2, 3, 4, 5, 1};
        int rotationCount = rotationCount(arr, 0, arr.length - 1);
        Assertions.assertEquals(4, rotationCount);
    }

    @Test
    void rotationCountTest3() {
        int[] arr = new int[]{1, 2, 3, 4, 5};
        int rotationCount = rotationCount(arr, 0, arr.length - 1);
        Assertions.assertEquals(-1, rotationCount);
    }
}

plugins {
    id 'java'
}

group = 'org.wesome'
version = '0.0.1-SNAPSHOT'
sourceCompatibility = JavaVersion.VERSION_1_8

repositories {
    mavenCentral()
}
dependencies {
    testImplementation('org.junit.jupiter:junit-jupiter:5.6.2')
}

test {
    useJUnitPlatform()
}