From 1d8bbb7a39cdab23a1ea4eeec93de79e56d22489 Mon Sep 17 00:00:00 2001
From: Marco Edward Gorelli <marcogorelli@protonmail.com>
Date: Thu, 20 Feb 2025 17:18:47 +0000
Subject: [PATCH] BUG: fix error message for multiindex.fillna (#60974)

fix error message for multiindex.fillna
---
 doc/source/whatsnew/v3.0.0.rst             | 1 +
 pandas/core/indexes/multi.py               | 2 +-
 pandas/tests/base/test_fillna.py           | 2 +-
 pandas/tests/indexes/multi/test_missing.py | 2 +-
 pandas/tests/indexes/test_old_base.py      | 2 +-
 5 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/doc/source/whatsnew/v3.0.0.rst b/doc/source/whatsnew/v3.0.0.rst
index 090be6dc250ba..999c2ebf32cc9 100644
--- a/doc/source/whatsnew/v3.0.0.rst
+++ b/doc/source/whatsnew/v3.0.0.rst
@@ -817,6 +817,7 @@ Other
 - Bug in :meth:`DataFrame.transform` that was returning the wrong order unless the index was monotonically increasing. (:issue:`57069`)
 - Bug in :meth:`DataFrame.where` where using a non-bool type array in the function would return a ``ValueError`` instead of a ``TypeError`` (:issue:`56330`)
 - Bug in :meth:`Index.sort_values` when passing a key function that turns values into tuples, e.g. ``key=natsort.natsort_key``, would raise ``TypeError`` (:issue:`56081`)
+- Bug in :meth:`MultiIndex.fillna` error message was referring to ``isna`` instead of ``fillna`` (:issue:`60974`)
 - Bug in :meth:`Series.diff` allowing non-integer values for the ``periods`` argument. (:issue:`56607`)
 - Bug in :meth:`Series.dt` methods in :class:`ArrowDtype` that were returning incorrect values. (:issue:`57355`)
 - Bug in :meth:`Series.isin` raising ``TypeError`` when series is large (>10**6) and ``values`` contains NA (:issue:`60678`)
diff --git a/pandas/core/indexes/multi.py b/pandas/core/indexes/multi.py
index dc48cd1ed958e..1cb984b5389d8 100644
--- a/pandas/core/indexes/multi.py
+++ b/pandas/core/indexes/multi.py
@@ -1760,7 +1760,7 @@ def fillna(self, value):
         """
         fillna is not implemented for MultiIndex
         """
-        raise NotImplementedError("isna is not defined for MultiIndex")
+        raise NotImplementedError("fillna is not defined for MultiIndex")
 
     @doc(Index.dropna)
     def dropna(self, how: AnyAll = "any") -> MultiIndex:
diff --git a/pandas/tests/base/test_fillna.py b/pandas/tests/base/test_fillna.py
index 7300d3013305a..8c56bcc169d8e 100644
--- a/pandas/tests/base/test_fillna.py
+++ b/pandas/tests/base/test_fillna.py
@@ -16,7 +16,7 @@ def test_fillna(index_or_series_obj):
     obj = index_or_series_obj
 
     if isinstance(obj, MultiIndex):
-        msg = "isna is not defined for MultiIndex"
+        msg = "fillna is not defined for MultiIndex"
         with pytest.raises(NotImplementedError, match=msg):
             obj.fillna(0)
         return
diff --git a/pandas/tests/indexes/multi/test_missing.py b/pandas/tests/indexes/multi/test_missing.py
index 14ffc42fb4b59..41cfa093ae53c 100644
--- a/pandas/tests/indexes/multi/test_missing.py
+++ b/pandas/tests/indexes/multi/test_missing.py
@@ -8,7 +8,7 @@
 
 def test_fillna(idx):
     # GH 11343
-    msg = "isna is not defined for MultiIndex"
+    msg = "fillna is not defined for MultiIndex"
     with pytest.raises(NotImplementedError, match=msg):
         idx.fillna(idx[0])
 
diff --git a/pandas/tests/indexes/test_old_base.py b/pandas/tests/indexes/test_old_base.py
index 49609d28ca56e..5f36b8c3f5dbf 100644
--- a/pandas/tests/indexes/test_old_base.py
+++ b/pandas/tests/indexes/test_old_base.py
@@ -597,7 +597,7 @@ def test_fillna(self, index):
             pytest.skip(f"Not relevant for Index with {index.dtype}")
         elif isinstance(index, MultiIndex):
             idx = index.copy(deep=True)
-            msg = "isna is not defined for MultiIndex"
+            msg = "fillna is not defined for MultiIndex"
             with pytest.raises(NotImplementedError, match=msg):
                 idx.fillna(idx[0])
         else: