feat: add unit tests for core functionality (#35)

requirements-dev.txt

@@ -0,0 +1 @@
+pytest>=8.0.0

tests/test_utils.py

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+import pytest
+from utils import calculate_average, find_max, normalize, parse_int_list
+
+def test_calculate_average():
+    assert calculate_average([1, 2, 3]) == 2.0
+    assert calculate_average([10, 20]) == 15.0
+    with pytest.raises(ValueError, match="Cannot calculate average of an empty list"):
+        calculate_average([])
+
+def test_find_max():
+    assert find_max([1, 5, 3]) == 5
+    assert find_max([-10, -5, -20]) == -5
+    with pytest.raises(ValueError, match="Cannot find max of an empty list"):
+        find_max([])
+
+def test_normalize():
+    assert normalize([0, 5, 10]) == [0.0, 0.5, 1.0]
+    with pytest.raises(ValueError, match="Cannot normalize an empty list"):
+        normalize([])
+    with pytest.raises(ValueError, match="Cannot normalize a constant list"):
+        normalize([5, 5, 5])
+
+def test_parse_int_list():
+    assert parse_int_list("1, 2, 3") == [1, 2, 3]
+    assert parse_int_list("10") == [10]
+    with pytest.raises(ValueError, match="Input string is empty"):
+        parse_int_list("")
+    with pytest.raises(ValueError, match="Input string is empty"):
+        parse_int_list("   ")
+    with pytest.raises(ValueError, match="invalid integer"):
+        parse_int_list("1, a, 3")