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a6a5d8e | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 | # SPDX-License-Identifier: Apache-2.0
"""Tests for a11oy.formulas.welford (Welford 1962). thesis_v22.pdf §2."""
import statistics
from a11oy.formulas import welford
def test_mean_variance_matches_numpy_style():
data = [10.0, 12.0, 23.0, 23.0, 16.0, 23.0, 21.0, 16.0]
w = welford.Welford()
for x in data:
w.update(x)
assert abs(w.mean - statistics.mean(data)) < 1e-9
assert abs(w.variance - statistics.variance(data)) < 1e-9
def test_zero_variance_before_two_samples():
w = welford.Welford()
w.update(5.0)
assert w.variance == 0.0
assert w.zscore(99.0) == 0.0
def test_anomaly_flag():
w = welford.Welford(z_threshold=3.0)
for _ in range(50):
w.update(100.0)
w.update(100.5)
assert w.is_anomaly(1000.0) is True
def test_observe_schema():
w = welford.Welford()
out = w.observe(1.0)
assert out["citation"] == "thesis_v22.pdf §2"
assert "welford_mean_exact" in out["lean_theorem"]
assert out["count"] == 1
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