Add unit tests for the "How Many Numbers Are Smaller Than the Current Number" problem.

src/main/java/com/leetcode/easy/HowManyNumbersAreSmallerThanTheCurrentNumber1365.java

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+// Tags: Array
+package com.leetcode.easy;
+
+public class HowManyNumbersAreSmallerThanTheCurrentNumber1365 {
+    /**
+     * Time Complexity: O(n²) where n is the length of the nums array
+     * - Outer loop iterates through all n elements
+     * - Inner loop also iterates through all n elements for each outer iteration
+     * - Total operations: n * n = n²
+     * <p>
+     * Space Complexity: O(n)
+     * - Result array 'res' stores n elements
+     * - Only uses constant extra space for variables (i, j, count)
+     */
+    public int[] smallerNumbersThanCurrent(int[] nums) {
+        int[] res = new int[nums.length];
+        for (int i = 0; i < nums.length; i++) {
+            int count = 0;
+            for (int j = 0; j < nums.length; j++) {
+                if (i != j && nums[j] < nums[i]) {
+                    count++;
+                }
+            }
+            res[i] = count;
+        }
+        return res;
+    }
+}

src/test/java/com/leetcode/easy/HowManyNumbersAreSmallerThanTheCurrentNumber1365Test.java

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+package com.leetcode.easy;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertArrayEquals;
+
+public class HowManyNumbersAreSmallerThanTheCurrentNumber1365Test {
+    private HowManyNumbersAreSmallerThanTheCurrentNumber1365 solution;
+
+    @BeforeEach
+    void setUp() {
+        solution = new HowManyNumbersAreSmallerThanTheCurrentNumber1365();
+    }
+
+    @Test
+    void testSmallerNumbersThanCurrent_Example1() {
+        int[] nums = {8, 1, 2, 2, 3};
+        int[] expected = {4, 0, 1, 1, 3};
+        int[] result = solution.smallerNumbersThanCurrent(nums);
+        assertArrayEquals(expected, result);
+    }
+
+    @Test
+    void testSmallerNumbersThanCurrent_Example2() {
+        int[] nums = {6, 5, 4, 8};
+        int[] expected = {2, 1, 0, 3};
+        int[] result = solution.smallerNumbersThanCurrent(nums);
+        assertArrayEquals(expected, result);
+    }
+
+    @Test
+    void testSmallerNumbersThanCurrent_Example3() {
+        int[] nums = {7, 7, 7, 7};
+        int[] expected = {0, 0, 0, 0};
+        int[] result = solution.smallerNumbersThanCurrent(nums);
+        assertArrayEquals(expected, result);
+    }
+}