Fix bug with modifiying polars object (#31)

* Learning how to modify polars dataframes; this is why i should learn polars fully :) 
* Add tests

src/iranges/IRanges.py

@@ -2200,7 +2200,7 @@ def to_polars(self) -> "polars.DataFrame":
             output = pl.concat([output, self._mcols.to_polars()])
 
         if self._names is not None:
-            output["rownames"] = self._names
+            output = output.with_columns(names=self._names)
 
         return output
 

tests/test_IRanges_polars.py

@@ -8,7 +8,7 @@
 __license__ = "MIT"
 
 
-def test_pandas():
+def test_from_polars():
     df = pl.DataFrame({"start": [1, 2, 3, 4], "width": [4, 5, 6, 7]})
 
     x = IRanges.from_polars(df)
@@ -17,10 +17,21 @@ def test_pandas():
     assert isinstance(x.mcols, BiocFrame)
 
 
-def test_pandas_export():
+def test_to_polars_export():
     x = IRanges([1, 2, 3, 4], [4, 5, 6, 7])
 
     y = x.to_polars()
     assert y is not None
     assert isinstance(y, pl.DataFrame)
     assert set(y.columns).issubset(["starts", "ends", "widths"])
+
+
+def test_to_polars_names():
+    x = IRanges(
+        [1, 2, 3, 4], [4, 5, 6, 7], names=["range1", "range2", "range3", "range4"]
+    )
+
+    y = x.to_polars()
+    assert y is not None
+    assert isinstance(y, pl.DataFrame)
+    assert set(y.columns).issubset(["starts", "ends", "widths", "names"])