Patch DEFAULT_BUFFER_HEURISTIC in test_warn_if_chunks_have_mismatched_type

Author: mroeschke

pandas/tests/io/parser/common/test_chunksize.py

@@ -229,17 +229,20 @@ def test_chunks_have_consistent_numerical_type(all_parsers, monkeypatch):
     assert result.a.dtype == float
 
 
-def test_warn_if_chunks_have_mismatched_type(all_parsers, using_infer_string):
+def test_warn_if_chunks_have_mismatched_type(
+    all_parsers, using_infer_string, monkeypatch
+):
     warning_type = None
     parser = all_parsers
-    size = 10000
+    heuristic = 2**3
+    size = 10
 
     # see gh-3866: if chunks are different types and can't
     # be coerced using numerical types, then issue warning.
     if parser.engine == "c" and parser.low_memory:
         warning_type = DtypeWarning
         # Use larger size to hit warning path
-        size = 499999
+        size = heuristic - 1
 
     integers = [str(i) for i in range(size)]
     data = "a\n" + "\n".join(integers + ["a", "b"] + integers)
@@ -251,12 +254,14 @@ def test_warn_if_chunks_have_mismatched_type(all_parsers, using_infer_string):
             buf,
         )
     else:
-        df = parser.read_csv_check_warnings(
-            warning_type,
-            r"Columns \(0: a\) have mixed types. "
-            "Specify dtype option on import or set low_memory=False.",
-            buf,
-        )
+        with monkeypatch.context() as m:
+            m.setattr(libparsers, "DEFAULT_BUFFER_HEURISTIC", heuristic)
+            df = parser.read_csv_check_warnings(
+                warning_type,
+                r"Columns \(0: a\) have mixed types. "
+                "Specify dtype option on import or set low_memory=False.",
+                buf,
+            )
     if parser.engine == "c" and parser.low_memory:
         assert df.a.dtype == object
     elif using_infer_string: