Add tests for Amicable Numbers (#3168)

src/test/java/com/thealgorithms/maths/AmicableNumberTest.java

@@ -0,0 +1,15 @@
+package com.thealgorithms.maths;
+
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class AmicableNumberTest {
+
+    @Test
+    void testAmicableNumber() {
+        assertThat(AmicableNumber.isAmicableNumber(220, 284)).isTrue();
+        assertThat(AmicableNumber.isAmicableNumber(1184, 1210)).isTrue();
+        assertThat(AmicableNumber.isAmicableNumber(2620, 2924)).isTrue();
+    }
+}