TST: stats: Added a regression test for stats.wilcoxon. Closes scipyg…

…h-2391.

scipy/stats/tests/test_morestats.py

@@ -533,5 +533,25 @@ def test_accuracy_wilcoxon():
     assert_allclose(p, 0.7240817, rtol=1e-6)
 
 
+def test_wilcoxon_tie():
+    # Regression test for gh-2391.
+    # Corresponding R code is:
+    #   > result = wilcox.test(rep(0.1, 10), exact=FALSE, correct=FALSE)
+    #   > result$p.value
+    #   [1] 0.001565402
+    #   > result = wilcox.test(rep(0.1, 10), exact=FALSE, correct=TRUE)
+    #   > result$p.value
+    #   [1] 0.001904195
+    stat, p = stats.wilcoxon([0.1] * 10)
+    expected_p = 0.001565402
+    assert_equal(stat, 0)
+    assert_allclose(p, expected_p, rtol=1e-6)
+
+    stat, p = stats.wilcoxon([0.1] * 10, correction=True)
+    expected_p = 0.001904195
+    assert_equal(stat, 0)
+    assert_allclose(p, expected_p, rtol=1e-6)
+
+
 if __name__ == "__main__":
     run_module_suite()