Improve code coverage by label_transfer tests

Checks if error is correctly raised when no KNN is present in adata.

tests/tools/_perturbation_space/test_simple_perturbation_space.py

@@ -240,9 +240,12 @@ def test_label_transfer():
  adata = AnnData(X)
  perturbations = np.array(["A", "B", "C"] * 22 + ["unknown"] * 3)
  adata.obs["perturbation"] = perturbations
- sc.pp.neighbors(adata, use_rep="X")
- sc.tl.umap(adata)
 
+ with pytest.raises(ValueError):
+ ps = pt.tl.PseudobulkSpace()
+ ps.label_transfer(adata)
+
+ sc.pp.neighbors(adata, use_rep="X")
  ps = pt.tl.PseudobulkSpace()
  ps.label_transfer(adata)
  assert "unknown" not in adata.obs["perturbation"]