Add testcase with negative size value

Author: dykov

src/test/java/io/github/dgroup/enumerable4j/AfterTest.java

@@ -30,6 +30,7 @@
 import org.llorllale.cactoos.matchers.Assertion;
 import org.llorllale.cactoos.matchers.HasSize;
 import org.llorllale.cactoos.matchers.HasValues;
+import org.llorllale.cactoos.matchers.Throws;
 
 /**
  * Test cases for {@link Enumerable#after}.
@@ -140,4 +141,13 @@ void nullPredicateAndZeroSize() {
         ).affirm();
     }
 
+    @Test
+    void throwExceptionOnNegativeSize() {
+        new Assertion<>(
+            "Must throw IllegalArgumentException if the size value is negative",
+            () -> new Linked<>(1, 2, 3).after(null, -1),
+            new Throws<>("-1", IllegalArgumentException.class)
+        ).affirm();
+    }
+
 }