add getBelow() in Matchfield - case: nothingBelow

src/main/java/de/tims/fleetstorm/matchfield/Matchfield.java

@@ -63,7 +63,9 @@ public class Matchfield {
 	}
 
 	public Coordinate getBelow(Coordinate center) {
-		// TODO Auto-generated method stub
+		if (center.getY() == 0) {
+			return null;
+		}
 		return matchfield[center.getX()][center.getY() - 1];
 	}
 

src/test/java/de/tims/fleetstorm/matchfield/MatchfieldCreationTest.java

@@ -122,7 +122,9 @@ class MatchfieldCreationTest {
 
 	static Stream<Arguments> getCoordinateBelow() {
 		Matchfield matchfield = new Matchfield(10);
-		return Stream.of(Arguments.of("below from (5/5) - should be (5,4)", matchfield, new Coordinate(5, 5),
-				matchfield.getField(5, 4)));
+		return Stream.of(
+				Arguments.of("below from (5/5) - should be (5,4)", matchfield, new Coordinate(5, 5),
+						matchfield.getField(5, 4)),
+				Arguments.of("below from (5/0) - should be null", matchfield, new Coordinate(5, 0), null));
 	}
 }