refactor: cleanup PigeonholeSort (#5298)

* refactor: PigeonholeSort

* checkstyle: fix formatting

* checkstyle: make class final

* refactor: changing negative numbers check first, fix typo, adding one more test for negative numbers

---------

Co-authored-by: Alex Klymenko <alx@alx.com>
Co-authored-by: vil02 <65706193+vil02@users.noreply.github.com>

src/test/java/com/thealgorithms/sorts/PigeonholeSortTest.java

@@ -0,0 +1,31 @@
+package com.thealgorithms.sorts;
+
+import static org.junit.jupiter.api.Assertions.assertArrayEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import java.util.stream.Stream;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.Arguments;
+import org.junit.jupiter.params.provider.MethodSource;
+
+public class PigeonholeSortTest {
+
+    @ParameterizedTest
+    @MethodSource("provideArraysForPigeonholeSort")
+    public void testPigeonholeSort(int[] inputArray, int[] expectedArray) {
+        PigeonholeSort.sort(inputArray);
+        assertArrayEquals(expectedArray, inputArray);
+    }
+
+    private static Stream<Arguments> provideArraysForPigeonholeSort() {
+        return Stream.of(Arguments.of(new int[] {}, new int[] {}), Arguments.of(new int[] {4}, new int[] {4}), Arguments.of(new int[] {6, 1, 99, 27, 15, 23, 36}, new int[] {1, 6, 15, 23, 27, 36, 99}), Arguments.of(new int[] {6, 1, 27, 15, 23, 27, 36, 23}, new int[] {1, 6, 15, 23, 23, 27, 27, 36}),
+            Arguments.of(new int[] {5, 5, 5, 5, 5}, new int[] {5, 5, 5, 5, 5}), Arguments.of(new int[] {1, 2, 3, 4, 5}, new int[] {1, 2, 3, 4, 5}), Arguments.of(new int[] {5, 4, 3, 2, 1}, new int[] {1, 2, 3, 4, 5}));
+    }
+
+    @Test
+    public void testWithNegativeNumbers() {
+        assertThrows(IllegalArgumentException.class, () -> PigeonholeSort.sort(new int[] {3, 1, 4, 1, 5, -9}));
+        assertThrows(IllegalArgumentException.class, () -> PigeonholeSort.sort(new int[] {-1}));
+    }
+}