Fix errors found in Functions (#273)

* Exercise 2.3: checks for unsupported units

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* fix units and decimals in ex2

---------

Co-authored-by: Adamopoulou <despoina.adamopoulou@empa.ch>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Author: 3 people

03_functions.ipynb

@@ -489,7 +489,7 @@
     "\n",
     "*Hint:* you can use the [built-in function](https://docs.python.org/3/library/functions.html#round) `round(number, ndigits)` function to round the floating point `number` to a given number expressed by `ndigits`.\n",
     "\n",
-    "Example: `length=2`, `width=3` should return `\"6.00 cm^2\"`\n",
+    "Example: `length=1.5`, `width=2.57` should return `\"3.85 cm^2\"`\n",
     "\n",
     "<div class=\"alert alert-block alert-warning\">\n",
     "    <h4><b>Note</b></h4>\n",
@@ -515,7 +515,7 @@
     "\n",
     "    Returns:\n",
     "        - A string representing the area with 2 decimal places,\n",
-    "          followed by \"cm^2\" (e.g., \"6.00 cm^2\")\n",
+    "          followed by \"cm^2\" (e.g., \"3.85 cm^2\")\n",
     "    \"\"\"\n",
     "    return"
    ]
@@ -528,12 +528,14 @@
     "### Part 2\n",
     "\n",
     "Extend the previous function, now called `solution_calculate_metric_area`, by adding a `unit` parameter that can be either \"cm\" or \"m\".\n",
+    "The default `length` and `width` unit is centimeters (\"cm\").\n",
+    "\n",
     "If the unit is \"m\", convert the measurements to centimeters before calculating the area.\n",
     "The result should still be in cm^2.\n",
     "\n",
     "*Hint:* remember the [built-in function](https://docs.python.org/3/library/functions.html#round) `round(number, ndigits)`.\n",
     "\n",
-    "Example: `length=2`, `width=3`, `unit=\"m\"` should return `\"60000.00 cm^2\"` (because 2m × 3m = 6m² = 60000cm²)\n",
+    "Example: `length=2.0`, `width=3.0`, `unit=\"m\"` should return `\"60000.0 cm^2\"` (because 2m × 3m = 6m² = 60000cm²)\n",
     "\n",
     "<div class=\"alert alert-block alert-warning\">\n",
     "    <h4><b>Note</b></h4>\n",
@@ -573,7 +575,7 @@
     "### Part 3\n",
     "\n",
     "Extend the previous function, now called `solution_calculate_area`, to support the following units: cm, m, mm, yd, and ft.\n",
-    "The calculated area should always be in centimeters, so you need to take care of the appropriate conversions (when needed).\n",
+    "The calculated area should always be in cm^2, so you need to take care of the appropriate conversions (when needed).\n",
     "Keep the same string format for the result.\n",
     "\n",
     "Use the following conversion factors:\n",

tutorial/tests/test_03_functions.py

@@ -95,10 +95,10 @@ def validate_basic_area_signature(function_to_test) -> None:
 @pytest.mark.parametrize(
     "length,width",
     [
-        (2.0, 3.0),
+        (2.123, 3.456),
         (5.0, 4.0),
-        (1.5, 2.5),
-        (0.1, 0.1),
+        (1.5, 2.57),
+        (0.109, 0.103),
     ],
 )
 def test_calculate_basic_area(length: float, width: float, function_to_test):
@@ -234,6 +234,28 @@ def test_calculate_area(length, width, unit, function_to_test):
     assert expected == result, "Incorrect area calculation or formatting"
 
 
+@pytest.mark.parametrize(
+    "length,width,unit",
+    [
+        (2.0, 3.0, "km"),  # Invalid unit
+        (2.0, 3.0, ""),  # Empty unit
+        (2.0, 3.0, "CM"),  # Case sensitive check
+        (2.0, 3.0, "inches"),  # Another invalid unit
+    ],
+)
+def test_calculate_area_invalid_units(length, width, unit, function_to_test):
+    """Test that the function properly handles invalid units."""
+    validate_area_signature(function_to_test)
+    result = function_to_test(length, width, unit)
+    expected = f"Invalid unit: {unit}"
+    assert isinstance(result, str), (
+        "Result should be a string like 'Invalid unit: <unit>'"
+    )
+    assert result == expected, (
+        f"Expected '{expected}' for invalid unit '{unit}', got '{result}'"
+    )
+
+
 #
 # Exercise 3: summing anything
 #