Speed up a test

Author: jonashaag

pandas/io/formats/csvs.py

@@ -44,6 +44,9 @@
     from pandas.io.formats.format import DataFrameFormatter
 
 
+_DEFAULT_CHUNKSIZE_CELLS = 100_000
+
+
 class CSVFormatter:
     cols: np.ndarray
 
@@ -162,7 +165,7 @@ def _initialize_columns(self, cols: Sequence[Hashable] | None) -> np.ndarray:
 
     def _initialize_chunksize(self, chunksize: int | None) -> int:
         if chunksize is None:
-            return (100000 // (len(self.cols) or 1)) or 1
+            return (_DEFAULT_CHUNKSIZE_CELLS // (len(self.cols) or 1)) or 1
         return int(chunksize)
 
     @property

pandas/tests/frame/methods/test_to_csv.py

@@ -759,9 +759,11 @@ def test_to_csv_chunking(self, chunksize):
             tm.assert_frame_equal(rs, aa)
 
     @pytest.mark.slow
-    def test_to_csv_wide_frame_formatting(self):
+    def test_to_csv_wide_frame_formatting(self, monkeypatch):
         # Issue #8621
-        df = DataFrame(np.random.randn(1, 100010), columns=None, index=None)
+        n_cells = 1_000
+        monkeypatch.setattr("pandas.io.formats.csvs._DEFAULT_CHUNKSIZE_CELLS", n_cells)
+        df = DataFrame(np.random.randn(1, n_cells + 10), columns=None, index=None)
         with tm.ensure_clean() as filename:
             df.to_csv(filename, header=False, index=False)
             rs = read_csv(filename, header=None)