build.gradle

// idea specific
apply plugin: 'idea'
idea{
    project{
        languageLevel = '1.7'
    }
}
apply plugin:'groovy'
repositories{
    mavenLocal()
    mavenCentral()
}
dependencies{
    compile 'org.codehaus.groovy:groovy-all:2.1.5'
    testCompile 'junit:junit:4.10'
}

Finder.groovy

class Finder {
    /**
     * Simple Binary search implementation.
     * Author: Daniil
     * @param arr - list to search in
     * @param el - element to find
     * @return index of the found element, or -1 if there is no such element in
     * <code>arr</code> or of <code>arr</code> is empty or <code>null</code>
     */
    static int binarySearch(List arr, int el) {
        if (arr == null || arr.empty || (arr.size == 1 && arr[0] != el))
            return -1
        int pivot = (int) arr.size / 2
        if (arr[pivot] == el)
            return pivot
        else if (el < arr[pivot]) {
            int search = binarySearch(arr[0..pivot-1], el)
            return search >= 0 ? search : -1
        } else {
            int search = binarySearch(arr[1 + pivot..arr.size - 1], el)
            return search >= 0 ? search + pivot + 1 : -1
        }
    }

}

FinderTest.groovy

class FinderTest extends GroovyTestCase {
    private List list

    void setUp() {
        list = [1, 2, 7, 10, 40, 50, 350, 599]
    }

    void testBinarySearch1() {
        assert Finder.binarySearch(list, 1) == 0
    }

    void testBinarySearch2() {
        assert Finder.binarySearch(list, 2) == 1
    }

    void testBinarySearch3() {
        assert Finder.binarySearch(list, 7) == 2
    }

    void testBinarySearch4() {
        assert Finder.binarySearch(list, 10) == 3
    }

    void testBinarySearch5() {
        assert Finder.binarySearch(list, 40) == 4
    }

    void testBinarySearch6() {
        assert Finder.binarySearch(list, 50) == 5
    }

    void testBinarySearch7() {
        assert Finder.binarySearch(list, 350) == 6
    }

    void testBinarySearch8() {
        assert Finder.binarySearch(list, 599) == 7
    }

    void testNotFound() {
        assert Finder.binarySearch(list, 0) == -1
    }

    void testEmptyArray() {
        assert Finder.binarySearch([], 0) == -1
    }

    void testNullArray() {
        assert Finder.binarySearch(null, 0) == -1
    }
}