TST: ensuring bins in cut during tiling are predictably small

Author: Nikhil-Narayanan

pandas/tests/reshape/test_cut.py

@@ -410,6 +410,31 @@ def test_single_bin(data, length):
     tm.assert_series_equal(result, expected)
 
 
+def test_single_bin_edge_adjustment():
+    # gh-58517 - test edge adjustment when all values are the same
+    # mutation on _nbins_to_bins
+    data = [0.1, 0.1, 0.1]
+    result, bins = cut(data, 3, retbins=True)
+
+    # mutation would create large bin sizes
+    bin_range = bins[-1] - bins[0]
+    assert bin_range < 0.001
+
+    # Test negative values
+    data_neg = [-0.1, -0.1, -0.1]
+    result_neg, bins_neg = cut(data_neg, 3, retbins=True)
+
+    bin_range_neg = bins_neg[-1] - bins_neg[0]
+    assert bin_range_neg < 0.001
+
+    # Test very small values
+    data_tiny = [0.01, 0.01, 0.01]
+    result_tiny, bins_tiny = cut(data_tiny, 3, retbins=True)
+
+    bin_range_tiny = bins_tiny[-1] - bins_tiny[0]
+    assert bin_range_tiny < 0.0001
+
+
 @pytest.mark.parametrize(
     "array_1_writeable,array_2_writeable", [(True, True), (True, False), (False, False)]
 )