Method inlining example. (#6520)

* Method inlining example.

* Test added

core-java/src/test/java/com/baeldung/inlining/ConsecutiveNumbersSumUnitTest.java

@@ -0,0 +1,22 @@
+package com.baeldung.inlining;
+
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+
+public class ConsecutiveNumbersSumUnitTest {
+
+    private static final int TOTAL_NUMBERS = 10;
+
+    @Test
+    public void givenTotalIntegersNumber_whenSumCalculated_thenEquals() {
+        ConsecutiveNumbersSum consecutiveNumbersSum = new ConsecutiveNumbersSum(TOTAL_NUMBERS);
+        long expectedSum = calculateExpectedSum(TOTAL_NUMBERS);
+
+        assertEquals(expectedSum, consecutiveNumbersSum.getTotalSum());
+    }
+
+    private long calculateExpectedSum(int totalNumbers) {
+        return totalNumbers * (totalNumbers + 1) / 2;
+    }
+}