Add JUnit tests for QuickSelectMedianOfMedians

Author: LUKMANul

src/test/java/com/thealgorithms/divideandconquer/DeterministicQuickSelectTest.java

@@ -0,0 +1,32 @@
+package com.thealgorithms.divideandconquer;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import org.junit.jupiter.api.Test;
+
+public class QuickSelectMedianOfMediansTest {
+
+    @Test
+    public void testBasicCases() {
+        assertEquals(7, QuickSelectMedianOfMedians.quickSelect(new int[]{12, 3, 5, 7, 4, 19, 26}, 3));
+        assertEquals(4, QuickSelectMedianOfMedians.quickSelect(new int[]{4, 2, 5, 2, 7, 4, 3}, 4));
+        assertEquals(0, QuickSelectMedianOfMedians.quickSelect(new int[]{-5, -10, 0, 5, 10}, 2));
+        assertEquals(3, QuickSelectMedianOfMedians.quickSelect(new int[]{8, 3, 1}, 1));
+        assertEquals(10, QuickSelectMedianOfMedians.quickSelect(new int[]{10, 20, 30, 40, 50}, 0));
+        assertEquals(50, QuickSelectMedianOfMedians.quickSelect(new int[]{10, 20, 30, 40, 50}, 4));
+        assertEquals(42, QuickSelectMedianOfMedians.quickSelect(new int[]{42}, 0));
+    }
+
+    @Test
+    public void testInvalidInputs() {
+        assertThrows(IllegalArgumentException.class, () ->
+                QuickSelectMedianOfMedians.quickSelect(null, 0));
+        assertThrows(IllegalArgumentException.class, () ->
+                QuickSelectMedianOfMedians.quickSelect(new int[]{1, 2, 3}, -1));
+        assertThrows(IllegalArgumentException.class, () ->
+                QuickSelectMedianOfMedians.quickSelect(new int[]{1, 2, 3}, 3));
+        assertThrows(IllegalArgumentException.class, () ->
+                QuickSelectMedianOfMedians.quickSelect(new int[]{}, 0));
+    }
+}