test: test Titanic example more thoroughly (#22)

Closes #16.

### Summary of Changes

Now we also check
* number of rows
* schema
* which columns have missing values.

---------

Co-authored-by: lars-reimann <[email protected]>

pyproject.toml

@@ -36,3 +36,12 @@ mkdocs-jupyter = "^0.23.0"
 [build-system]
 requires = ["poetry-core"]
 build-backend = "poetry.core.masonry.api"
+
+[tool.pytest.ini_options]
+addopts = "--strict-markers"
+markers = [
+    "smoke: quickly testing core functionality",
+]
+
+[tool.black]
+line-length = 120

tests/safeds_examples/tabular/titanic/test_load_titanic.py

@@ -1,9 +1,46 @@
+import pytest
 from safeds.data.tabular import Table
+from safeds.data.tabular.typing import (
+    FloatColumnType,
+    IntColumnType,
+    StringColumnType,
+    TableSchema,
+)
 from safeds_examples.tabular import load_titanic
 
 
-def test_load_titanic() -> None:
-    titanic = load_titanic()
+class TestLoadTitanic:
+    @pytest.fixture
+    def titanic(self) -> Table:
+        return load_titanic()
 
-    assert isinstance(titanic, Table)
-    assert titanic.count_rows() > 0
+    @pytest.mark.smoke
+    def test_returns_table(self) -> None:
+        titanic = load_titanic()
+
+        assert isinstance(titanic, Table)
+
+    def test_row_count(self, titanic: Table) -> None:
+        assert titanic.count_rows() == 1309
+
+    def test_schema(self, titanic: Table) -> None:
+        assert titanic.schema == TableSchema(
+            {
+                "Age": FloatColumnType(),
+                "Cabin Number": StringColumnType(),
+                "Fare": FloatColumnType(),
+                "Name": StringColumnType(),
+                "Number of Parents or Children Aboard": IntColumnType(),
+                "Number of Siblings or Spouses Aboard": IntColumnType(),
+                "Port of Embarkation": StringColumnType(),
+                "Sex": StringColumnType(),
+                "Survived": IntColumnType(),
+                "Ticket Number": StringColumnType(),
+                "Travel Class": IntColumnType(),
+            }
+        )
+
+    def test_columns_with_missing_values(self, titanic: Table) -> None:
+        actual_column_names = {column.name for column in titanic.list_columns_with_missing_values()}
+
+        assert actual_column_names == {"Age", "Port of Embarkation", "Fare", "Cabin Number"}