Add unit tests for the "Richest Customer Wealth" problem.

src/main/java/com/leetcode/easy/RichestCustomerWealth1672.java

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+// Tags: Array, Matrix
+package com.leetcode.easy;
+
+public class RichestCustomerWealth1672 {
+    /*
+        Let M be the number of customers and N be the number of banks.
+        Time complexity: O(M⋅N)
+        For each of the M customers,
+        we need to iterate over all N banks to find the sum of his/her wealth.
+        Hence, the total time complexity is O(M⋅N).
+
+        Space complexity: O(1)
+        We only need two variables personWealth and maxWealthSoFar
+        to store the wealth of the current customer,
+        and the highest wealth we have seen so far respectively.
+        Therefore, the space complexity is constant.
+     */
+    public int maximumWealth(int[][] accounts) {
+        int maxWealthSoFar = 0;
+        for (int[] account : accounts) {
+            int personWealth = 0;
+            for (int money : account) {
+                personWealth += money;
+            }
+            maxWealthSoFar = Math.max(maxWealthSoFar, personWealth);
+        }
+        return maxWealthSoFar;
+    }
+}

src/test/java/com/leetcode/easy/RichestCustomerWealth1672Test.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.assertEquals;
+
+public class RichestCustomerWealth1672Test {
+    private RichestCustomerWealth1672 solution;
+
+    @BeforeEach
+    void setUp() {
+        solution = new RichestCustomerWealth1672();
+    }
+
+    @Test
+    void testMaximumWealth_Example1() {
+        int[][] accounts = {
+                {1, 2, 3},
+                {3, 2, 1}
+        };
+        int expected = 6;
+        int result = solution.maximumWealth(accounts);
+        assertEquals(expected, result);
+    }
+
+    @Test
+    void testMaximumWealth_Example2() {
+        int[][] accounts = {
+                {1, 5},
+                {7, 3},
+                {3, 5}
+        };
+        int expected = 10;
+        int result = solution.maximumWealth(accounts);
+        assertEquals(expected, result);
+    }
+
+    @Test
+    void testMaximumWealth_Example3() {
+        int[][] accounts = {
+                {2, 8, 7},
+                {7, 1, 3},
+                {1, 9, 5}
+        };
+        int expected = 17;
+        int result = solution.maximumWealth(accounts);
+        assertEquals(expected, result);
+    }
+}