gameexplorer: addPoints() increases / decreases points of player

src/main/java/de/tims/gameexplorer/Player.java

@@ -9,7 +9,7 @@ public class Player {
 	}
 
 	public void addPoints(int pointsToAdd) {
-		this.points = pointsToAdd;
+		this.points += pointsToAdd;
 	}
 
 	public int getPoints() {

src/test/java/de/tims/gameexplorer/PlayerTest.java

@@ -23,7 +23,9 @@ class PlayerTest {
 	
 	private static Stream<Arguments> testCasesForAddPoints() {
 		return Stream.of(Arguments.of("NoPointsBeforeGet0Points", 0, 0, 0),
-				Arguments.of("NoPointsBeforeGet10Points", 0, 10, 10));
+				Arguments.of("NoPointsBeforeGet10Points", 0, 10, 10),
+				Arguments.of("10PointsBeforeAdd10Points", 10, 10, 20),
+				Arguments.of("10PointsBeforeLose10Points", 10, -10, 0));
 	}
 
 }