test: improve coverage (#241)

### Summary of Changes

* Remove unused or outdated code
* Improve test coverage for remaining code

---------

Co-authored-by: megalinter-bot <129584137+megalinter-bot@users.noreply.github.com>

src/safeds/data/tabular/containers/_column.py

@@ -58,9 +58,6 @@ def __eq__(self, other: object) -> bool:
     def __getitem__(self, index: int) -> Any:
         return self.get_value(index)
 
-    def __hash__(self) -> int:
-        return hash(self._data)
-
     def __iter__(self) -> Iterator[Any]:
         return iter(self._data)
 

src/safeds/data/tabular/containers/_row.py

@@ -467,5 +467,4 @@ def _repr_html_(self) -> str:
         output : str
             The generated HTML.
         """
-        # noinspection PyProtectedMember
-        return self._data._repr_html_()
+        return self._data.to_html(max_rows=1, max_cols=self._data.shape[1], notebook=True)

src/safeds/data/tabular/containers/_tagged_table.py

@@ -1,7 +1,5 @@
 from collections.abc import Iterable
 
-from IPython.core.display_functions import DisplayHandle
-
 from safeds.data.tabular.containers import Column, Table
 from safeds.data.tabular.typing import Schema
 
@@ -50,16 +48,6 @@ def __init__(
         self._features: Table = self.keep_only_columns(feature_names)
         self._target: Column = self.get_column(target_name)
 
-    def __repr__(self) -> str:
-        tmp = self._features.add_column(self._target)
-        header_info = "Target Column is '" + self._target.name + "'\n"
-        return header_info + tmp.__repr__()
-
-    def __str__(self) -> str:
-        tmp = self._features.add_column(self._target)
-        header_info = "Target Column is '" + self._target.name + "'\n"
-        return header_info + tmp.__str__()
-
     # ------------------------------------------------------------------------------------------------------------------
     # Properties
     # ------------------------------------------------------------------------------------------------------------------
@@ -71,21 +59,3 @@ def features(self) -> Table:
     @property
     def target(self) -> Column:
         return self._target
-
-    # ------------------------------------------------------------------------------------------------------------------
-    # IPython integration
-    # ------------------------------------------------------------------------------------------------------------------
-
-    def _ipython_display_(self) -> DisplayHandle:
-        """
-        Return a display object for the column to be used in Jupyter Notebooks.
-
-        Returns
-        -------
-        output : DisplayHandle
-            Output object.
-        """
-        tmp = self._features.add_column(self._target)
-        header_info = "Target Column is '" + self._target.name + "'\n"
-        print(header_info)  # noqa: T201
-        return tmp._ipython_display_()

src/safeds/data/tabular/exceptions/__init__.py

@@ -6,7 +6,6 @@
     DuplicateColumnNameError,
     IndexOutOfBoundsError,
     MissingDataError,
-    MissingSchemaError,
     NonNumericColumnError,
     SchemaMismatchError,
     TransformerNotFittedError,
@@ -19,7 +18,6 @@
     "DuplicateColumnNameError",
     "IndexOutOfBoundsError",
     "MissingDataError",
-    "MissingSchemaError",
     "NonNumericColumnError",
     "SchemaMismatchError",
     "TransformerNotFittedError",

src/safeds/data/tabular/exceptions/_exceptions.py

@@ -73,13 +73,6 @@ def __init__(self) -> None:
         super().__init__("Failed because at least two schemas didn't match.")
 
 
-class MissingSchemaError(Exception):
-    """Exception raised when a required schema is missing."""
-
-    def __init__(self) -> None:
-        super().__init__("Failed because a required schema is missing.")
-
-
 class ColumnLengthMismatchError(Exception):
     """Exception raised when the lengths of two or more columns do not match."""
 

src/safeds/data/tabular/typing/_imputer_strategy.py

@@ -12,4 +12,11 @@ class ImputerStrategy(ABC):
 
     @abstractmethod
     def _augment_imputer(self, imputer: sk_SimpleImputer) -> None:
-        pass
+        """
+        Set the imputer strategy of the given imputer.
+
+        Parameters
+        ----------
+        imputer: SimpleImputer
+            The imputer to augment.
+        """

src/safeds/ml/exceptions/_exceptions.py

@@ -32,15 +32,12 @@ class LearningError(Exception):
 
     Parameters
     ----------
-    reason: str | None
+    reason: str
         The reason for the error.
     """
 
-    def __init__(self, reason: str | None):
-        if reason is None:
-            super().__init__("Error occurred while learning")
-        else:
-            super().__init__(f"Error occurred while learning: {reason}")
+    def __init__(self, reason: str):
+        super().__init__(f"Error occurred while learning: {reason}")
 
 
 class ModelNotFittedError(Exception):
@@ -56,12 +53,9 @@ class PredictionError(Exception):
 
     Parameters
     ----------
-    reason: str | None
+    reason: str
         The reason for the error.
     """
 
-    def __init__(self, reason: str | None):
-        if reason is None:
-            super().__init__("Error occurred while predicting")
-        else:
-            super().__init__(f"Error occurred while predicting: {reason}")
+    def __init__(self, reason: str):
+        super().__init__(f"Error occurred while predicting: {reason}")

tests/safeds/data/tabular/transformation/test_imputer.py

@@ -5,6 +5,21 @@
 from safeds.data.tabular.typing import ImputerStrategy
 
 
+class TestStrategy:
+    class TestStr:
+        @pytest.mark.parametrize(
+            ("strategy", "expected"),
+            [
+                (Imputer.Strategy.Constant(0), "Constant(0)"),
+                (Imputer.Strategy.Mean(), "Mean"),
+                (Imputer.Strategy.Median(), "Median"),
+                (Imputer.Strategy.Mode(), "Mode"),
+            ],
+        )
+        def test_should_return_correct_string_representation(self, strategy: ImputerStrategy, expected: str) -> None:
+            assert str(strategy) == expected
+
+
 class TestFit:
     def test_should_raise_if_column_not_found(self) -> None:
         table = Table.from_dict(