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diff --git a/tools/tests/test_gen_fuzz_corpus.py b/tools/tests/test_gen_fuzz_corpus.py
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+++ b/tools/tests/test_gen_fuzz_corpus.py
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+# Author:  cirakg & claude ai
+# Summary: Tests for the fuzz corpus generator: determinism, mutation, valid Monkey C output, and the committed corpus.
+from __future__ import annotations
+
+import random
+from pathlib import Path
+
+import gen_fuzz_corpus
+
+ROOT = Path(__file__).resolve().parents[2]
+
+
+def test_same_seed_gives_the_same_corpus() -> None:
+    assert gen_fuzz_corpus.corpus(7, 10, 10) == gen_fuzz_corpus.corpus(7, 10, 10)
+    assert gen_fuzz_corpus.corpus(7, 10, 10) != gen_fuzz_corpus.corpus(8, 10, 10)
+
+
+def test_corpus_starts_with_the_valid_seeds() -> None:
+    jsons, uris = gen_fuzz_corpus.corpus(1, 5, 5)
+    assert jsons[0] == gen_fuzz_corpus.AEGIS_SEED.encode()
+    assert uris[: len(gen_fuzz_corpus.URI_SEEDS)] == [u.encode() for u in gen_fuzz_corpus.URI_SEEDS]
+    assert len(jsons) == 5 and len(uris) == 5
+
+
+def test_mutate_changes_the_input() -> None:
+    rng = random.Random(3)
+    base = gen_fuzz_corpus.AEGIS_SEED.encode()
+    assert sum(gen_fuzz_corpus.mutate(base, rng) != base for _ in range(20)) >= 19
+
+
+def test_render_puts_commas_outside_the_comments() -> None:
+    text = gen_fuzz_corpus.render([b"{}", b"[]"], [b"x"], 1)
+    assert '"7b7d", // lint: allow-literal' in text
+    assert '"5b5d" // lint: allow-literal' in text
+    assert text.startswith("// Author:  cirakg & claude ai\n// Summary:")
+
+
+def test_committed_corpus_matches_the_generator() -> None:
+    jsons, uris = gen_fuzz_corpus.corpus(4242, 50, 50)
+    committed = (ROOT / "test" / "data" / "FuzzCorpus.mc").read_text(encoding="utf-8")
+    assert committed == gen_fuzz_corpus.render(jsons, uris, 4242)