test: add null value tests for StoryFileHandler

src/main/java/edu/ntnu/idatt2001/group_30/filehandling/StoryFileHandler.java

@@ -47,6 +47,7 @@ public class StoryFileHandler {
      */
     public void createStoryFile(Story story, String fileName) throws IOException {
         Objects.requireNonNull(story, "Story cannot be null");
+        Objects.requireNonNull(fileName, "File name cannot be null");
         File file = FileHandler.createFile(fileName);
         if(FileHandler.fileExists(file)) throw new IllegalArgumentException("You cannot overwrite a pre-existing story file");
         try(BufferedWriter storyBufferedWriter = new BufferedWriter(new FileWriter(file))){
@@ -61,6 +62,7 @@ public class StoryFileHandler {
      * @throws IOException  This exception is thrown if an I/O error occurs with the reader.
      */
     public Story readStoryFromFile(String fileName) throws IOException, InstantiationException {
+        Objects.requireNonNull(fileName, "File name cannot be null");
         File file = new File(FileHandler.getFileSourcePath(fileName));
         if(!FileHandler.fileExists(file)) throw new IllegalArgumentException("There is no story file with that name!");
         Story story;

src/test/java/edu/ntnu/idatt2001/group_30/filehandling/StoryFileHandlerTest.java

@@ -211,6 +211,22 @@ class StoryFileHandlerTest {
             });
         }
 
+        @Test
+        void a_null_file_name_when_creating_new_file_will_throw_NullPointerException(){
+            Story story = validStory();
+
+            Assertions.assertThrows(NullPointerException.class, () ->{
+                storyFileHandler.createStoryFile(story, null);
+            });
+        }
+
+        @Test
+        void a_null_file_name_when_reading_file_will_throw_NullPointerException(){
+            Assertions.assertThrows(NullPointerException.class, () ->{
+                Story story = storyFileHandler.readStoryFromFile(null);
+            });
+        }
+
         //TODO: change this actually test the link information
         @Test
         void corrupt_link_information_throws_CorruptLinkException_when_read(){