Add missing size validation test for last(int) (#25)

src/test/java/com/pivovarit/gatherers/LastTest.java

@@ -4,27 +4,36 @@
 
 import java.util.stream.Stream;
 
+import static com.pivovarit.gatherers.MoreGatherers.last;
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
 
 class LastTest {
 
+    @Test
+    void shouldRejectInvalidSize() {
+        assertThatThrownBy(() -> last(0))
+          .isInstanceOf(IllegalArgumentException.class)
+          .hasMessage("number of elements can't be lower than one");
+    }
+
     @Test
     void shouldLastEmpty() {
-        assertThat(Stream.of().gather(MoreGatherers.last(42))).isEmpty();
+        assertThat(Stream.of().gather(last(42))).isEmpty();
     }
 
     @Test
     void shouldTakeLastElement() {
-        assertThat(Stream.of(1, 2, 3).gather(MoreGatherers.last(1))).containsExactly(3);
+        assertThat(Stream.of(1, 2, 3).gather(last(1))).containsExactly(3);
     }
 
     @Test
     void shouldTakeLastNElements() {
-        assertThat(Stream.of(1, 2, 3).gather(MoreGatherers.last(2))).containsExactly(2, 3);
+        assertThat(Stream.of(1, 2, 3).gather(last(2))).containsExactly(2, 3);
     }
 
     @Test
     void shouldTakeLastAllElements() {
-        assertThat(Stream.of(1, 2, 3).gather(MoreGatherers.last(42))).containsExactly(1, 2, 3);
+        assertThat(Stream.of(1, 2, 3).gather(last(42))).containsExactly(1, 2, 3);
     }
 }