From 4fec5df8622c61a4a21cdcdc0b709aafa531b8fc Mon Sep 17 00:00:00 2001
From: louis <@>
Date: Sat, 2 Nov 2019 14:56:14 +0000
Subject: [PATCH 1/4] TST: Test for fix of type issue in empty groupby from
 DataFrame with categorical.

---
 pandas/tests/groupby/test_groupby.py | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/pandas/tests/groupby/test_groupby.py b/pandas/tests/groupby/test_groupby.py
index e17181f55fdba..fae272bbb0bdb 100644
--- a/pandas/tests/groupby/test_groupby.py
+++ b/pandas/tests/groupby/test_groupby.py
@@ -1825,6 +1825,18 @@ def test_groupby_empty_list_raises():
         df.groupby([[]])
 
 
+def test_groupby_with_empty_category():
+    # GH-9614
+    df = pd.DataFrame({"id": [None] * 3, "spam": [None] * 3})
+    df["spam"] = df["spam"].astype("category")
+    df["spam"] == "spam"  # works as expected
+    result = df.groupby("id").first()["spam"] == "spam"
+    expected = Series(
+        [], name="spam", dtype=bool, index=pd.Series([], dtype="object", name="id")
+    )
+    tm.assert_series_equal(result, expected)
+
+
 def test_groupby_multiindex_series_keys_len_equal_group_axis():
     # GH 25704
     index_array = [["x", "x"], ["a", "b"], ["k", "k"]]

From 3396aa7fbc0e62d96c5e253695ef815b406d21fe Mon Sep 17 00:00:00 2001
From: louis <@>
Date: Sat, 2 Nov 2019 23:48:25 +0000
Subject: [PATCH 2/4] TST: Refactor test for empty groupby with categorical
 data.

---
 pandas/tests/groupby/test_categorical.py | 12 ++++++++++++
 pandas/tests/groupby/test_groupby.py     | 12 ------------
 2 files changed, 12 insertions(+), 12 deletions(-)

diff --git a/pandas/tests/groupby/test_categorical.py b/pandas/tests/groupby/test_categorical.py
index 22a23407b2521..1b92615bf6ac0 100644
--- a/pandas/tests/groupby/test_categorical.py
+++ b/pandas/tests/groupby/test_categorical.py
@@ -781,6 +781,18 @@ def test_categorical_no_compress():
     tm.assert_numpy_array_equal(result, exp)
 
 
+def test_groupby_empty_with_category():
+    # GH-9614
+    df = pd.DataFrame({"A": [None] * 3, "B": pd.Categorical(["train", "train", "test"])})
+    result = df.groupby("A").first()["B"]
+    expected = pd.Series(
+        pd.Categorical([], categories=["test", "train"]),
+        index=pd.Series([], dtype="object", name="A"),
+        name="B",
+    )
+    tm.assert_series_equal(result, expected)
+
+
 def test_sort():
 
     # http://stackoverflow.com/questions/23814368/sorting-pandas-
diff --git a/pandas/tests/groupby/test_groupby.py b/pandas/tests/groupby/test_groupby.py
index fae272bbb0bdb..e17181f55fdba 100644
--- a/pandas/tests/groupby/test_groupby.py
+++ b/pandas/tests/groupby/test_groupby.py
@@ -1825,18 +1825,6 @@ def test_groupby_empty_list_raises():
         df.groupby([[]])
 
 
-def test_groupby_with_empty_category():
-    # GH-9614
-    df = pd.DataFrame({"id": [None] * 3, "spam": [None] * 3})
-    df["spam"] = df["spam"].astype("category")
-    df["spam"] == "spam"  # works as expected
-    result = df.groupby("id").first()["spam"] == "spam"
-    expected = Series(
-        [], name="spam", dtype=bool, index=pd.Series([], dtype="object", name="id")
-    )
-    tm.assert_series_equal(result, expected)
-
-
 def test_groupby_multiindex_series_keys_len_equal_group_axis():
     # GH 25704
     index_array = [["x", "x"], ["a", "b"], ["k", "k"]]

From 18293ab35c18e81bc529a2cbd23acd31efb0fbf5 Mon Sep 17 00:00:00 2001
From: louis <@>
Date: Sun, 3 Nov 2019 00:04:34 +0000
Subject: [PATCH 3/4] TST: Refactor test for empty groupby with categorical
 data.

---
 pandas/tests/groupby/test_categorical.py | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/pandas/tests/groupby/test_categorical.py b/pandas/tests/groupby/test_categorical.py
index 1b92615bf6ac0..7577167ccfe3e 100644
--- a/pandas/tests/groupby/test_categorical.py
+++ b/pandas/tests/groupby/test_categorical.py
@@ -783,7 +783,9 @@ def test_categorical_no_compress():
 
 def test_groupby_empty_with_category():
     # GH-9614
-    df = pd.DataFrame({"A": [None] * 3, "B": pd.Categorical(["train", "train", "test"])})
+    df = pd.DataFrame(
+        {"A": [None] * 3, "B": pd.Categorical(["train", "train", "test"])}
+    )
     result = df.groupby("A").first()["B"]
     expected = pd.Series(
         pd.Categorical([], categories=["test", "train"]),

From 4b77aaa9ea242872fc1828097d80ca651bbe3397 Mon Sep 17 00:00:00 2001
From: louis <@>
Date: Sun, 3 Nov 2019 08:38:29 +0000
Subject: [PATCH 4/4] Add test comment to re-trigger build.

---
 pandas/tests/groupby/test_categorical.py | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/pandas/tests/groupby/test_categorical.py b/pandas/tests/groupby/test_categorical.py
index 7577167ccfe3e..a187781ea214c 100644
--- a/pandas/tests/groupby/test_categorical.py
+++ b/pandas/tests/groupby/test_categorical.py
@@ -783,6 +783,8 @@ def test_categorical_no_compress():
 
 def test_groupby_empty_with_category():
     # GH-9614
+    # test fix for when group by on None resulted in
+    # coercion of dtype categorical -> float
     df = pd.DataFrame(
         {"A": [None] * 3, "B": pd.Categorical(["train", "train", "test"])}
     )