TST: Add a test for comparing the signatures of `nan<x>` and `<x>` functions

1 files changed, 48 insertions, 0 deletions

diff --git a/numpy/lib/tests/test_nanfunctions.py b/numpy/lib/tests/test_nanfunctions.py
index 3fdeec41c..3b0fa6656 100644
--- a/numpy/lib/tests/test_nanfunctions.py
+++ b/numpy/lib/tests/test_nanfunctions.py
@@ -1,5 +1,6 @@
 import warnings
 import pytest
+import inspect
 
 import numpy as np
 from numpy.lib.nanfunctions import _nan_mask, _replace_nan
@@ -35,6 +36,53 @@ _ndat_zeros = np.array([[0.6244, 0.0, 0.2692, 0.0116, 0.0, 0.1170],
                         [0.1610, 0.0, 0.0, 0.1859, 0.3146, 0.0]])
 
 
+class TestSignatureMatch:
+    NANFUNCS = {
+        np.nanmin: np.amin,
+        np.nanmax: np.amax,
+        np.nanargmin: np.argmin,
+        np.nanargmax: np.argmax,
+        np.nansum: np.sum,
+        np.nanprod: np.prod,
+        np.nancumsum: np.cumsum,
+        np.nancumprod: np.cumprod,
+        np.nanmean: np.mean,
+        np.nanmedian: np.median,
+        np.nanpercentile: np.percentile,
+        np.nanquantile: np.quantile,
+        np.nanvar: np.var,
+        np.nanstd: np.std,
+    }
+    IDS = [k.__name__ for k in NANFUNCS]
+
+    @staticmethod
+    def get_signature(func, default="..."):
+        """Construct a signature and replace all default parameter-values."""
+        prm_list = []
+        signature = inspect.signature(func)
+        for prm in signature.parameters.values():
+            if prm.default is inspect.Parameter.empty:
+                prm_list.append(prm)
+            else:
+                prm_list.append(prm.replace(default=default))
+        return inspect.Signature(prm_list)
+
+    @pytest.mark.parametrize("nan_func,func", NANFUNCS.items(), ids=IDS)
+    def test_signature_match(self, nan_func, func):
+        # Ignore the default parameter-values as they can sometimes differ
+        # between the two functions (*e.g.* one has `False` while the other
+        # has `np._NoValue`)
+        signature = self.get_signature(func)
+        nan_signature = self.get_signature(nan_func)
+        np.testing.assert_equal(signature, nan_signature)
+
+    def test_exhaustiveness(self):
+        """Validate that all nan functions are actually tested."""
+        np.testing.assert_equal(
+            set(self.IDS), set(np.lib.nanfunctions.__all__)
+        )
+
+
 class TestNanFunctions_MinMax:
 
     nanfuncs = [np.nanmin, np.nanmax]