Add a multi-language mutation tester that writes .metrics/mutate for uml-viewer.

tests/test_edn.py

@@ -0,0 +1,55 @@
+from mutator.edn import dumps, keyword, loads
+
+
+def test_round_trip_matches_the_snapshot_shape():
+    payload = {
+        "version": 1,
+        "tested-at": "2026-09-30T12:00:00-05:00",
+        "source": 'src/demo/say "hi".py',
+        "namespace": "demo.Board",
+        "outcomes": {
+            '["src/a.py","demo.Board","defn/place",1,2,">",">="]': keyword("killed"),
+            '["src/a.py","demo.Board","defn-/hide",3,4,"true","false"]': keyword("survived"),
+        },
+        "forms": [
+            {
+                "id": "defn/place",
+                "kind": "defn",
+                "file": "src/demo/Board.java",
+                "line": 4,
+                "end-line": 9,
+                "hash": "abc",
+                "killed": 1,
+                "survived": 0,
+                "uncovered": 2,
+                "sites": 3,
+            }
+        ],
+    }
+    text = dumps(payload)
+    assert text.startswith("{")
+    assert ":namespace" in text
+    assert ":killed" in text
+    parsed = loads(text)
+    assert parsed["namespace"] == "demo.Board"
+    assert parsed["forms"][0]["id"] == "defn/place"
+    assert parsed["forms"][0]["end-line"] == 9
+    assert parsed["forms"][0]["killed"] == 1
+    assert set(parsed["outcomes"].values()) == {"killed", "survived"}
+
+
+def test_empty_collections_and_nil():
+    assert loads("{:forms [] :outcomes {} :note nil}") == {
+        "forms": [],
+        "outcomes": {},
+        "note": None,
+    }
+
+
+def test_atoms_cover_booleans_numbers_and_symbols():
+    assert loads("true") is True
+    assert loads("false") is False
+    assert loads("12") == 12
+    assert loads("-3") == -3
+    assert loads("1.50") == 1.5
+    assert loads("foo") == "foo"