diff --git a/src/piqtree/iqtree/_model_finder.py b/src/piqtree/iqtree/_model_finder.py
index a187983..afd14ab 100644
--- a/src/piqtree/iqtree/_model_finder.py
+++ b/src/piqtree/iqtree/_model_finder.py
@@ -101,7 +101,10 @@ def __post_init__(self, raw_data: dict[str, Any]) -> None:
     def to_rich_dict(self) -> dict[str, Any]:
         import piqtree
 
-        result = {"version": piqtree.__version__, "type": get_object_provenance(self)}
+        result: dict[str, Any] = {
+            "version": piqtree.__version__,
+            "type": get_object_provenance(self),
+        }
 
         raw_data = {
             str(model_): f"{stats.lnL} {stats.nfp} {stats.tree_length}"
@@ -109,6 +112,7 @@ def to_rich_dict(self) -> dict[str, Any]:
         }
         for attr in ("best_model_AIC", "best_model_AICc", "best_model_BIC"):
             raw_data[attr] = str(getattr(self, attr.replace("_model", "").lower()))
+
         result["init_kwargs"] = {"raw_data": raw_data, "source": self.source}
         return result
 
diff --git a/tests/test_iqtree/test_fit_tree.py b/tests/test_iqtree/test_fit_tree.py
index 1ef00cf..14fe653 100644
--- a/tests/test_iqtree/test_fit_tree.py
+++ b/tests/test_iqtree/test_fit_tree.py
@@ -1,3 +1,5 @@
+from typing import cast
+
 import numpy as np
 import pytest
 from cogent3 import get_app, make_tree
@@ -14,18 +16,18 @@ def check_likelihood(got: PhyloNode, expected: model_result) -> None:
 
 
 def check_motif_probs(got: PhyloNode, expected: PhyloNode) -> None:
-    expected = expected.params["mprobs"]
-    got = got.params["mprobs"]
+    expected_mprobs = expected.params["mprobs"]
+    got_mprobs = got.params["mprobs"]
 
-    expected_keys = set(expected.keys())
-    got_keys = set(got.keys())
+    expected_keys = set(expected_mprobs.keys())
+    got_keys = set(got_mprobs.keys())
 
     # Check that the base characters are the same
     assert expected_keys == got_keys
 
     # Check that the probs are the same
-    expected_values = [expected[key] for key in expected_keys]
-    got_values = [got[key] for key in expected_keys]
+    expected_values = [expected_mprobs[key] for key in expected_keys]
+    got_values = [got_mprobs[key] for key in expected_keys]
     assert all(
         got == pytest.approx(exp)
         for got, exp in zip(got_values, expected_values, strict=True)
@@ -54,16 +56,16 @@ def check_rate_parameters(got: PhyloNode, expected: PhyloNode) -> None:
 
 
 def check_branch_lengths(got: PhyloNode, expected: PhyloNode) -> None:
-    got = got.tip_to_tip_distances()
-    expected = expected.tip_to_tip_distances()
+    got_dists = got.tip_to_tip_distances()
+    expected_dists = expected.tip_to_tip_distances()
     # make sure the distance matrices have the same name order
     # so we can just compare entire numpy arrays
-    expected = expected.take_dists(got.names)
+    expected_dists = expected_dists.take_dists(got_dists.names)
     # Check that the keys of branch lengths are the same
-    assert set(got.names) == set(expected.names)
+    assert set(got_dists.names) == set(expected_dists.names)
 
     # Check that the branch lengths are the same
-    np.testing.assert_allclose(got.array, expected.array, atol=1e-4)
+    np.testing.assert_allclose(got_dists.array, expected_dists.array, atol=1e-4)
 
 
 @pytest.mark.parametrize(
@@ -178,7 +180,7 @@ def test_fit_tree_paramaterisation(three_otu: Alignment, model_str: str) -> None
 
     assert isinstance(tree.params["lnL"], float)
     for node in tree.preorder(include_self=False):
-        assert node.length > 0
+        assert cast("float", node.length) > 0
 
 
 def test_special_characters(three_otu: Alignment) -> None:
@@ -194,6 +196,6 @@ def _renamer(before: str) -> str:
 
     assert isinstance(tree.params["lnL"], float)
     for node in tree.preorder(include_self=False):
-        assert node.length > 0
+        assert cast("float", node.length) > 0
 
     assert set(three_otu.names) == set(tree.get_tip_names())
diff --git a/tests/test_iqtree/test_nj_tree.py b/tests/test_iqtree/test_nj_tree.py
index 33c1416..2685d7a 100644
--- a/tests/test_iqtree/test_nj_tree.py
+++ b/tests/test_iqtree/test_nj_tree.py
@@ -1,4 +1,5 @@
 import re
+from typing import cast
 
 import numpy as np
 import pytest
@@ -23,11 +24,15 @@ def test_nj_tree_allow_negative(all_otu: Alignment) -> None:
 
     # check that all branch lengths are non-negative, by default
     tree1 = nj_tree(dists)
-    assert all(node.length >= 0 for node in tree1.preorder(include_self=False))
+    assert all(
+        cast("float", node.length) >= 0 for node in tree1.preorder(include_self=False)
+    )
 
     # check that some branch lengths are negative when allow_negative=True
     tree2 = nj_tree(dists, allow_negative=True)
-    assert any(node.length < 0 for node in tree2.preorder(include_self=False))
+    assert any(
+        cast("float", node.length) < 0 for node in tree2.preorder(include_self=False)
+    )
 
 
 def test_nj_tree_nan(four_otu: Alignment) -> None:
diff --git a/tests/test_iqtree/test_tree_yaml.py b/tests/test_iqtree/test_tree_yaml.py
index 47989d7..e10d542 100644
--- a/tests/test_iqtree/test_tree_yaml.py
+++ b/tests/test_iqtree/test_tree_yaml.py
@@ -277,5 +277,5 @@ def test_unrest_model(
 )
 def test_tree_equal(candidate: str, expected: bool) -> None:
     tree = make_tree("((a:1.0,b:0.9),c:0.8);")
-    candidate = make_tree(candidate)
-    assert _tree_equal(tree, candidate) == expected
+    candidate_tree = make_tree(candidate)
+    assert _tree_equal(tree, candidate_tree) == expected