diff --git a/codebeaver.yml b/codebeaver.yml
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--- /dev/null
+++ b/codebeaver.yml
@@ -0,0 +1,2 @@
+from:pytest
+# This file was generated automatically by CodeBeaver based on your repository. Learn how to customize it here: https://docs.codebeaver.ai/configuration/
\ No newline at end of file
diff --git a/tests/test_expense_tracker.py b/tests/test_expense_tracker.py
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+++ b/tests/test_expense_tracker.py
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+import pytest
+from expense_tracker import (
+    ExpenseTracker,
+    main,
+)
+
+
+def test_default_properties():
+    """
+    Test that a newly created ExpenseTracker instance has the default properties.
+    Specifically, verify that the 'expenses' list is empty and that the 'categories'
+    set contains the expected default categories: "food", "transport", "utilities",
+    "entertainment", and "other".
+    """
+    tracker = ExpenseTracker()
+    assert tracker.expenses == []
+    expected_categories = {"food", "transport", "utilities", "entertainment", "other"}
+    assert tracker.categories == expected_categories
+
+
+def test_main_output(capsys):
+    """
+    Test that when main() is called, it prints 'nothing here yet' to stdout.
+    """
+    main()
+    captured = capsys.readouterr()
+    assert captured.out == "nothing here yet\n"
+
+
+def test_add_expense():
+    """
+    Test that an expense can be directly added to the 'expenses' list of an ExpenseTracker instance.
+    This simulates adding an expense record (e.g., a dictionary) to verify that the list is mutable
+    and retains the newly added expense.
+    """
+    tracker = ExpenseTracker()
+    expense = {"amount": 50, "category": "food"}
+    tracker.expenses.append(expense)
+    assert tracker.expenses == [expense]
+
+
+def test_instance_independence():
+    """
+    Test that two ExpenseTracker instances have independent 'expenses' lists and 'categories' sets.
+    Modifying one instance does not affect the properties of the other instance.
+    """
+    tracker1 = ExpenseTracker()
+    tracker2 = ExpenseTracker()
+    tracker1.expenses.append({"amount": 20, "category": "transport"})
+    tracker1.categories.add("new_category")
+    assert tracker2.expenses == []
+    expected_categories = {"food", "transport", "utilities", "entertainment", "other"}
+    assert tracker2.categories == expected_categories
+
+
+def test_instance_unique_objects():
+    """
+    Test that each ExpenseTracker instance has its own unique 'expenses' list and 'categories' set.
+    This helps to confirm that modifications in one instance do not affect the other due to
+    shared mutable objects.
+    """
+    tracker1 = ExpenseTracker()
+    tracker2 = ExpenseTracker()
+    assert tracker1.expenses is not tracker2.expenses
+    assert tracker1.categories is not tracker2.categories
+
+
+def test_property_types():
+    """
+    Test that a newly created ExpenseTracker instance has properties of the correct types.
+    Specifically, verify that 'expenses' is a list and 'categories' is a set.
+    """
+    tracker = ExpenseTracker()
+    assert isinstance(tracker.expenses, list), "'expenses' should be a list"
+    assert isinstance(tracker.categories, set), "'categories' should be a set"
+
+
+def test_append_different_types():
+    """
+    Test that various types of objects can be appended to the 'expenses' list
+    without errors, since the ExpenseTracker class does not enforce any type validation
+    for the expense records.
+    """
+    tracker = ExpenseTracker()
+    sample_items = [42, "A random expense", [1, 2, 3], {"nested": "dict"}]
+    for item in sample_items:
+        tracker.expenses.append(item)
+    assert tracker.expenses == sample_items
+
+
+def test_expenses_order():
+    """
+    Test that the 'expenses' list maintains the insertion order.
+    This test appends several expense records and verifies the order is preserved.
+    """
+    tracker = ExpenseTracker()
+    expense1 = {"amount": 30, "category": "food"}
+    expense2 = {"amount": 15, "category": "transport"}
+    expense3 = {"amount": 60, "category": "utilities"}
+    tracker.expenses.append(expense1)
+    tracker.expenses.append(expense2)
+    tracker.expenses.append(expense3)
+    expected_order = [expense1, expense2, expense3]
+    assert tracker.expenses == expected_order
+
+
+def test_main_called_twice(capsys):
+    """
+    Test that calling main() twice separately prints 'nothing here yet'
+    each time to stdout, ensuring consistent behavior on multiple calls.
+    """
+    main()
+    captured_first = capsys.readouterr()
+    assert captured_first.out == "nothing here yet\n"
+    main()
+    captured_second = capsys.readouterr()
+    assert captured_second.out == "nothing here yet\n"
+
+
+def test_expenses_order_after_removal():
+    """
+    Test that after removing an expense, the order of the remaining expenses is preserved.
+    This test appends three expense records to the tracker, removes the middle one, and verifies that
+    the order of the remaining records is as expected.
+    """
+    tracker = ExpenseTracker()
+    expense1 = {"amount": 40, "category": "food"}
+    expense2 = {"amount": 25, "category": "transport"}
+    expense3 = {"amount": 15, "category": "utilities"}
+    tracker.expenses.append(expense1)
+    tracker.expenses.append(expense2)
+    tracker.expenses.append(expense3)
+    tracker.expenses.remove(expense2)
+    expected_order = [expense1, expense3]
+    assert tracker.expenses == expected_order