Merged PR 164: File System Class setup fixing tests

## Summary
Attempting to fix a test which seems to be broken when integrated with https://dev.azure.com/ma-dev-uk/PrimAITE/_git/PrimAITE/pullrequest/160

## Test process
*How have you tested this (if applicable)?*

## Checklist
- [x] This PR is linked to a **work item**
- [x] I have performed **self-review** of the code
- [x] I have written **tests** for any new functionality added with this PR
- [ ] I have updated the **documentation** if this PR changes or adds functionality
- [ ] I have written/updated **design docs** if this PR implements new functionality.
- [x] I have run **pre-commit** checks for code style

#1714: fixing minor error in test + adding a check for existing uuid when adding file

Related work items: #1714

tests/unit_tests/_primaite/_simulator/_file_system/test_file_system.py

@@ -1,4 +1,5 @@
 from primaite.simulator.file_system.file_system import FileSystem
+from primaite.simulator.file_system.file_system_file import FileSystemFile
 from primaite.simulator.file_system.file_system_folder import FileSystemFolder
 
 
@@ -37,7 +38,7 @@ def test_delete_file():
 
     file_system.delete_file(file=file)
     assert len(file_system.folders) is 1
-    assert len(file_system.get_folder_by_id(folder.uuid).files) is 0
+    assert len(folder.files) is 0
 
 
 def test_delete_non_existent_file():
@@ -45,16 +46,20 @@ def test_delete_non_existent_file():
     file_system = FileSystem()
 
     file = file_system.create_file(file_name="test_file", size=10)
-    not_added_file = file_system.create_file(file_name="test_file", size=10)
+    not_added_file = FileSystemFile(name="not_added")
+    # folder should be created
     assert len(file_system.folders) is 1
-
+    # should only have 1 file in the file system
     folder_id = list(file_system.folders.keys())[0]
     folder = file_system.get_folder_by_id(folder_id)
+    assert len(list(folder.files)) is 1
+
     assert folder.get_file_by_id(file.uuid) is file
 
+    # deleting should not change how many files are in folder
     file_system.delete_file(file=not_added_file)
     assert len(file_system.folders) is 1
-    assert len(file_system.get_folder_by_id(folder.uuid).files) is 1
+    assert len(list(folder.files)) is 1
 
 
 def test_delete_folder():