diff --git a/shell.nix b/shell.nix
index 5c0cd0d..ec82a6c 100644
--- a/shell.nix
+++ b/shell.nix
@@ -33,6 +33,7 @@ in
 
     (pkgs.python3.withPackages (ps: [
       ps.pytest
+      ps.black
     ]))
 
   ];
diff --git a/tests/test_eval.py b/tests/test_eval.py
index 48bba7c..68dca79 100644
--- a/tests/test_eval.py
+++ b/tests/test_eval.py
@@ -30,11 +30,11 @@ def common_test(extra_args: List[str]) -> None:
         assert built_job["name"] == "job1"
         assert built_job["outputs"]["out"].startswith("/nix/store")
         assert built_job["drvPath"].endswith(".drv")
-        assert built_job["meta"]['broken'] is False
+        assert built_job["meta"]["broken"] is False
 
         dotted_job = results[1]
-        assert dotted_job["attr"] == "\"dotted.attr\""
-        assert dotted_job["attrPath"] == [ "dotted.attr" ]
+        assert dotted_job["attr"] == '"dotted.attr"'
+        assert dotted_job["attrPath"] == ["dotted.attr"]
 
         recurse_drv = results[2]
         assert recurse_drv["attr"] == "recurse.drvB"
@@ -46,7 +46,7 @@ def common_test(extra_args: List[str]) -> None:
         substituted_job = results[4]
         assert substituted_job["attr"] == "substitutedJob"
         assert substituted_job["name"].startswith("hello-")
-        assert substituted_job["meta"]['broken'] is False
+        assert substituted_job["meta"]["broken"] is False
 
 
 def test_flake() -> None:
diff --git a/treefmt.toml b/treefmt.toml
index d1280df..19a28ed 100644
--- a/treefmt.toml
+++ b/treefmt.toml
@@ -15,3 +15,7 @@ includes = ["*.nix"]
 command = "prettier"
 options = ["--write"]
 includes = ["*.toml"]
+
+[formatter.python]
+command = "black"
+includes = ["*.py"]