Add tests for SumOfArithmeticSeries (#4256)

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

@@ -0,0 +1,53 @@
+package com.thealgorithms.maths;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import org.junit.jupiter.api.Test;
+
+public class SumOfArithmeticSeriesTest {
+    @Test
+    public void testSumFrom1To10() {
+        assertEquals(55.0, SumOfArithmeticSeries.sumOfSeries(1.0, 1.0, 10));
+    }
+
+    @Test
+    public void testSumOfOddNumbers1To19() {
+        assertEquals(100.0, SumOfArithmeticSeries.sumOfSeries(1.0, 2.0, 10));
+    }
+
+    @Test
+    public void testA() {
+        assertEquals(460.0, SumOfArithmeticSeries.sumOfSeries(1.0, 10.0, 10));
+    }
+
+    @Test
+    public void testB() {
+        assertEquals(5.5, SumOfArithmeticSeries.sumOfSeries(0.1, 0.1, 10));
+    }
+
+    @Test
+    public void testC() {
+        assertEquals(49600.0, SumOfArithmeticSeries.sumOfSeries(1, 10, 100));
+    }
+
+    @Test
+    public void testForZeroTerms() {
+        assertEquals(0.0, SumOfArithmeticSeries.sumOfSeries(1.0, 100.0, 0), 0.00001);
+    }
+
+    @Test
+    public void testIfThrowsExceptionForNegativeNumberOfTerms() {
+        assertThrows(IllegalArgumentException.class, () -> SumOfArithmeticSeries.sumOfSeries(1.0, 1.0, -1));
+    }
+
+    @Test
+    public void testWithSingleTerm() {
+        assertEquals(123.0, SumOfArithmeticSeries.sumOfSeries(123.0, 5.0, 1));
+    }
+
+    @Test
+    public void testWithZeroCommonDiff() {
+        assertEquals(100.0, SumOfArithmeticSeries.sumOfSeries(1.0, 0.0, 100));
+    }
+}