fuzzy testing with pysource_codegen

scripts/find_issue.py

@@ -0,0 +1,55 @@
+from pathlib import Path
+
+from pysource_codegen import generate
+from pysource_minimize import minimize
+
+import black
+
+base_path = Path(__file__).parent
+
+
+def bug_in_code(src_contents: str, mode: black.FileMode) -> bool:
+    try:
+        dst_contents = black.format_str(src_contents, mode=mode)
+
+        black.assert_equivalent(src_contents, dst_contents)
+        black.assert_stable(src_contents, dst_contents, mode=mode)
+    except Exception as e:
+        print("error:", e)
+        return True
+    return False
+
+
+def find_issue() -> None:
+    mode = black.FileMode(
+        line_length=80,
+        string_normalization=True,
+        is_pyi=False,
+        magic_trailing_comma=False,
+    )
+    for seed in range(1000):
+        src_code = generate(seed)
+        print("seed:", seed)
+
+        compile(src_code, "<string>", "exec")
+
+        if bug_in_code(src_code, mode):
+            minimized = minimize(src_code, lambda code: bug_in_code(code, mode))
+            assert bug_in_code(minimized, mode)
+
+            print("seed:", seed)
+            print("minimized code:")
+            print(minimized)
+
+            if "with" in minimized:
+                # propably known issue
+                # https://github.com/psf/black/issues/3678
+                # https://github.com/psf/black/issues/3677
+                continue
+
+            (base_path / "min_code.py").write_text(minimized)
+            return
+
+
+if __name__ == "__main__":
+    find_issue()

test_requirements.txt

@@ -4,3 +4,5 @@ pytest >= 6.1.1
 pytest-xdist >= 3.0.2
 pytest-cov >= 4.1.0
 tox
+pysource_codegen >= 0.4.1
+pysource_minimize >= 0.4.0