From 66433d5bb66f808b97fd91a701819878684d7a37 Mon Sep 17 00:00:00 2001
From: Avinash Pancham <avinashpancham@outlook.com>
Date: Sat, 20 Jun 2020 12:36:15 +0200
Subject: [PATCH 1/6] TST: Ensure dtypes are set correctly for empty integer
 columns #24386

---
 pandas/tests/dtypes/test_dtypes.py | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/pandas/tests/dtypes/test_dtypes.py b/pandas/tests/dtypes/test_dtypes.py
index b1fe673e9e2f1..e91409b27cf1d 100644
--- a/pandas/tests/dtypes/test_dtypes.py
+++ b/pandas/tests/dtypes/test_dtypes.py
@@ -991,3 +991,8 @@ def test_is_dtype_no_warning(check):
 
     with tm.assert_produces_warning(None):
         check(data["A"])
+
+
+def test_check_dtype_empty_column():
+    data = pd.DataFrame({"a": [1, 2]}, columns=["b"], dtype=int)
+    assert data.b.dtype is np.dtype("int")

From feb768002a4d0a747688236fadeec568fd1f1163 Mon Sep 17 00:00:00 2001
From: Avinash Pancham <avinashpancham@outlook.com>
Date: Sat, 20 Jun 2020 14:00:58 +0200
Subject: [PATCH 2/6] Add comment to refer to GH issue tracker

---
 pandas/tests/dtypes/test_dtypes.py | 1 +
 1 file changed, 1 insertion(+)

diff --git a/pandas/tests/dtypes/test_dtypes.py b/pandas/tests/dtypes/test_dtypes.py
index e91409b27cf1d..748d9b9d398dc 100644
--- a/pandas/tests/dtypes/test_dtypes.py
+++ b/pandas/tests/dtypes/test_dtypes.py
@@ -994,5 +994,6 @@ def test_is_dtype_no_warning(check):
 
 
 def test_check_dtype_empty_column():
+    # GH24386: Ensure dtypes are set correctly for empty integer columns
     data = pd.DataFrame({"a": [1, 2]}, columns=["b"], dtype=int)
     assert data.b.dtype is np.dtype("int")

From 3c2f72bd7bef6d64173ff866fb3d712cef8b416b Mon Sep 17 00:00:00 2001
From: Avinash Pancham <avinashpancham@outlook.com>
Date: Sat, 20 Jun 2020 14:04:30 +0200
Subject: [PATCH 3/6] Refactor check, use == instead of is

---
 pandas/tests/dtypes/test_dtypes.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pandas/tests/dtypes/test_dtypes.py b/pandas/tests/dtypes/test_dtypes.py
index 748d9b9d398dc..d8ac7ba429506 100644
--- a/pandas/tests/dtypes/test_dtypes.py
+++ b/pandas/tests/dtypes/test_dtypes.py
@@ -996,4 +996,4 @@ def test_is_dtype_no_warning(check):
 def test_check_dtype_empty_column():
     # GH24386: Ensure dtypes are set correctly for empty integer columns
     data = pd.DataFrame({"a": [1, 2]}, columns=["b"], dtype=int)
-    assert data.b.dtype is np.dtype("int")
+    assert data.b.dtype == np.dtype("int")

From 8c682945cf1675d9e04c5269c63fbf6257bd76e4 Mon Sep 17 00:00:00 2001
From: Avinash Pancham <avinashpancham@outlook.com>
Date: Sat, 20 Jun 2020 14:58:24 +0200
Subject: [PATCH 4/6] Moved file to test_constructors.py and added test for
 other dtypes

---
 pandas/tests/dtypes/test_dtypes.py      |  6 ------
 pandas/tests/frame/test_constructors.py | 26 +++++++++++++++++++++++++
 2 files changed, 26 insertions(+), 6 deletions(-)

diff --git a/pandas/tests/dtypes/test_dtypes.py b/pandas/tests/dtypes/test_dtypes.py
index d8ac7ba429506..b1fe673e9e2f1 100644
--- a/pandas/tests/dtypes/test_dtypes.py
+++ b/pandas/tests/dtypes/test_dtypes.py
@@ -991,9 +991,3 @@ def test_is_dtype_no_warning(check):
 
     with tm.assert_produces_warning(None):
         check(data["A"])
-
-
-def test_check_dtype_empty_column():
-    # GH24386: Ensure dtypes are set correctly for empty integer columns
-    data = pd.DataFrame({"a": [1, 2]}, columns=["b"], dtype=int)
-    assert data.b.dtype == np.dtype("int")
diff --git a/pandas/tests/frame/test_constructors.py b/pandas/tests/frame/test_constructors.py
index baac87755c6d2..61c601662a853 100644
--- a/pandas/tests/frame/test_constructors.py
+++ b/pandas/tests/frame/test_constructors.py
@@ -18,6 +18,7 @@
 import pandas as pd
 from pandas import (
     Categorical,
+    CategoricalDtype,
     DataFrame,
     Index,
     MultiIndex,
@@ -2245,6 +2246,31 @@ def test_from_records_empty_with_nonempty_fields_gh3682(self):
         tm.assert_index_equal(df.index, Index([], name="id"))
         assert df.index.name == "id"
 
+    @pytest.mark.parametrize(
+        "input_value, expected_value",
+        [
+            ("int16", np.dtype("int16")),
+            ("int32", np.dtype("int32")),
+            ("int64", np.dtype("int64")),
+            ("float16", np.dtype("float16")),
+            ("float32", np.dtype("float32")),
+            ("float64", np.dtype("float64")),
+            ("uint16", np.dtype("uint16")),
+            ("uint32", np.dtype("uint32")),
+            ("uint64", np.dtype("uint64")),
+            ("datetime64[ns]", np.dtype("<M8[ns]")),
+            ("timedelta64[ns]", np.dtype("<m8[ns]")),
+            ("bool", np.dtype("bool")),
+            ("object", np.dtype("O")),
+            ("category", CategoricalDtype(categories=[], ordered=False)),
+        ],
+    )
+    def test_check_dtype_empty_column(self, input_value, expected_value):
+        # GH24386: Ensure dtypes are set correctly for an empty DataFrame.
+        # Empty DataFrame is generated via dictionary data with non-overlapping columns.
+        data = pd.DataFrame({"a": [1, 2]}, columns=["b"], dtype=input_value)
+        assert data.b.dtype == expected_value
+
     def test_from_records_with_datetimes(self):
 
         # this may fail on certain platforms because of a numpy issue

From 9a41ab89b934a4aa06089a0650f175e977a22466 Mon Sep 17 00:00:00 2001
From: Avinash Pancham <avinashpancham@outlook.com>
Date: Sat, 20 Jun 2020 15:57:51 +0200
Subject: [PATCH 5/6] Add support for more dtypes

---
 pandas/tests/frame/test_constructors.py | 89 +++++++++++++++++++++++--
 1 file changed, 85 insertions(+), 4 deletions(-)

diff --git a/pandas/tests/frame/test_constructors.py b/pandas/tests/frame/test_constructors.py
index 61c601662a853..aff9332ed8307 100644
--- a/pandas/tests/frame/test_constructors.py
+++ b/pandas/tests/frame/test_constructors.py
@@ -21,11 +21,19 @@
     CategoricalDtype,
     DataFrame,
     Index,
+    Int8Dtype,
+    Int16Dtype,
+    Int32Dtype,
+    Int64Dtype,
     MultiIndex,
     RangeIndex,
     Series,
     Timedelta,
     Timestamp,
+    UInt8Dtype,
+    UInt16Dtype,
+    UInt32Dtype,
+    UInt64Dtype,
     date_range,
     isna,
 )
@@ -2249,20 +2257,93 @@ def test_from_records_empty_with_nonempty_fields_gh3682(self):
     @pytest.mark.parametrize(
         "input_value, expected_value",
         [
+            # Unsigned int datatype
+            ("uint8", np.dtype("uint8")),
+            ("uint16", np.dtype("uint16")),
+            ("uint32", np.dtype("uint32")),
+            ("uint64", np.dtype("uint64")),
+            (np.dtype("uint8"), np.dtype("uint8")),
+            (np.dtype("uint16"), np.dtype("uint16")),
+            (np.dtype("uint32"), np.dtype("uint32")),
+            (np.dtype("uint64"), np.dtype("uint64")),
+            # Unsigned ea int datatype
+            ("UInt8", UInt8Dtype()),
+            ("UInt16", UInt16Dtype()),
+            ("UInt32", UInt32Dtype()),
+            ("UInt64", UInt64Dtype()),
+            (UInt8Dtype(), UInt8Dtype()),
+            (UInt16Dtype(), UInt16Dtype()),
+            (UInt32Dtype(), UInt32Dtype()),
+            (UInt64Dtype(), UInt64Dtype()),
+            # Int datatype
+            (int, np.dtype("int64")),
+            ("int", np.dtype("int64")),
+            ("int8", np.dtype("int8")),
             ("int16", np.dtype("int16")),
             ("int32", np.dtype("int32")),
             ("int64", np.dtype("int64")),
+            (np.dtype("int8"), np.dtype("int8")),
+            (np.dtype("int16"), np.dtype("int16")),
+            (np.dtype("int32"), np.dtype("int32")),
+            (np.dtype("int64"), np.dtype("int64")),
+            # Int ea datatype
+            ("Int8", Int8Dtype()),
+            ("Int16", Int16Dtype()),
+            ("Int32", Int32Dtype()),
+            ("Int64", Int64Dtype()),
+            (Int8Dtype(), Int8Dtype()),
+            (Int16Dtype(), Int16Dtype()),
+            (Int32Dtype(), Int32Dtype()),
+            (Int64Dtype(), Int64Dtype()),
+            # Floats
+            (float, np.dtype("float64")),
+            ("float", np.dtype("float64")),
             ("float16", np.dtype("float16")),
             ("float32", np.dtype("float32")),
             ("float64", np.dtype("float64")),
-            ("uint16", np.dtype("uint16")),
-            ("uint32", np.dtype("uint32")),
-            ("uint64", np.dtype("uint64")),
+            ("Float16", np.dtype("float16")),
+            ("Float32", np.dtype("float32")),
+            ("Float64", np.dtype("float64")),
+            (np.dtype("float16"), np.dtype("float16")),
+            (np.dtype("float32"), np.dtype("float32")),
+            (np.dtype("float64"), np.dtype("float64")),
+            # Complex
+            (complex, np.dtype("complex128")),
+            ("complex", np.dtype("complex128")),
+            ("complex64", np.dtype("complex64")),
+            ("complex128", np.dtype("complex128")),
+            ("complex256", np.dtype("complex256")),
+            ("Complex64", np.dtype("complex128")),
+            ("Complex128", np.dtype("complex256")),
+            (np.dtype("complex64"), np.dtype("complex64")),
+            (np.dtype("complex128"), np.dtype("complex128")),
+            (np.dtype("complex256"), np.dtype("complex256")),
+            # Strings
+            (str, np.dtype("O")),
+            (bytes, np.dtype("O")),
+            ("str", np.dtype("O")),
+            ("bytes", np.dtype("O")),
+            ("U", np.dtype("O")),
+            ("object", np.dtype("O")),
+            ("bytes", np.dtype("O")),
+            (np.dtype("O"), np.dtype("O")),
+            # Datetime-like objects
+            ("M8[ns]", np.dtype("<M8[ns]")),
             ("datetime64[ns]", np.dtype("<M8[ns]")),
+            (np.dtype("<M8[ns]"), np.dtype("<M8[ns]")),
+            ("m8[ns]", np.dtype("<m8[ns]")),
             ("timedelta64[ns]", np.dtype("<m8[ns]")),
+            (np.dtype("<m8[ns]"), np.dtype("<m8[ns]")),
+            # Boolean
+            (bool, np.dtype("bool")),
             ("bool", np.dtype("bool")),
-            ("object", np.dtype("O")),
+            (np.dtype("bool"), np.dtype("bool")),
+            # Categorical
             ("category", CategoricalDtype(categories=[], ordered=False)),
+            (
+                CategoricalDtype(categories=[], ordered=False),
+                CategoricalDtype(categories=[], ordered=False),
+            ),
         ],
     )
     def test_check_dtype_empty_column(self, input_value, expected_value):

From d2dfa8b4ef558295d5cd1e524d14176633fa02e7 Mon Sep 17 00:00:00 2001
From: Avinash Pancham <avinashpancham@outlook.com>
Date: Sat, 20 Jun 2020 17:12:19 +0200
Subject: [PATCH 6/6] Refactor testing for data types using containers in
 _testing.py

---
 pandas/tests/frame/test_constructors.py | 124 +++++-------------------
 1 file changed, 22 insertions(+), 102 deletions(-)

diff --git a/pandas/tests/frame/test_constructors.py b/pandas/tests/frame/test_constructors.py
index aff9332ed8307..6207b270faefc 100644
--- a/pandas/tests/frame/test_constructors.py
+++ b/pandas/tests/frame/test_constructors.py
@@ -18,22 +18,13 @@
 import pandas as pd
 from pandas import (
     Categorical,
-    CategoricalDtype,
     DataFrame,
     Index,
-    Int8Dtype,
-    Int16Dtype,
-    Int32Dtype,
-    Int64Dtype,
     MultiIndex,
     RangeIndex,
     Series,
     Timedelta,
     Timestamp,
-    UInt8Dtype,
-    UInt16Dtype,
-    UInt32Dtype,
-    UInt64Dtype,
     date_range,
     isna,
 )
@@ -2255,102 +2246,31 @@ def test_from_records_empty_with_nonempty_fields_gh3682(self):
         assert df.index.name == "id"
 
     @pytest.mark.parametrize(
-        "input_value, expected_value",
-        [
-            # Unsigned int datatype
-            ("uint8", np.dtype("uint8")),
-            ("uint16", np.dtype("uint16")),
-            ("uint32", np.dtype("uint32")),
-            ("uint64", np.dtype("uint64")),
-            (np.dtype("uint8"), np.dtype("uint8")),
-            (np.dtype("uint16"), np.dtype("uint16")),
-            (np.dtype("uint32"), np.dtype("uint32")),
-            (np.dtype("uint64"), np.dtype("uint64")),
-            # Unsigned ea int datatype
-            ("UInt8", UInt8Dtype()),
-            ("UInt16", UInt16Dtype()),
-            ("UInt32", UInt32Dtype()),
-            ("UInt64", UInt64Dtype()),
-            (UInt8Dtype(), UInt8Dtype()),
-            (UInt16Dtype(), UInt16Dtype()),
-            (UInt32Dtype(), UInt32Dtype()),
-            (UInt64Dtype(), UInt64Dtype()),
-            # Int datatype
-            (int, np.dtype("int64")),
-            ("int", np.dtype("int64")),
-            ("int8", np.dtype("int8")),
-            ("int16", np.dtype("int16")),
-            ("int32", np.dtype("int32")),
-            ("int64", np.dtype("int64")),
-            (np.dtype("int8"), np.dtype("int8")),
-            (np.dtype("int16"), np.dtype("int16")),
-            (np.dtype("int32"), np.dtype("int32")),
-            (np.dtype("int64"), np.dtype("int64")),
-            # Int ea datatype
-            ("Int8", Int8Dtype()),
-            ("Int16", Int16Dtype()),
-            ("Int32", Int32Dtype()),
-            ("Int64", Int64Dtype()),
-            (Int8Dtype(), Int8Dtype()),
-            (Int16Dtype(), Int16Dtype()),
-            (Int32Dtype(), Int32Dtype()),
-            (Int64Dtype(), Int64Dtype()),
-            # Floats
-            (float, np.dtype("float64")),
-            ("float", np.dtype("float64")),
-            ("float16", np.dtype("float16")),
-            ("float32", np.dtype("float32")),
-            ("float64", np.dtype("float64")),
-            ("Float16", np.dtype("float16")),
-            ("Float32", np.dtype("float32")),
-            ("Float64", np.dtype("float64")),
-            (np.dtype("float16"), np.dtype("float16")),
-            (np.dtype("float32"), np.dtype("float32")),
-            (np.dtype("float64"), np.dtype("float64")),
-            # Complex
-            (complex, np.dtype("complex128")),
-            ("complex", np.dtype("complex128")),
-            ("complex64", np.dtype("complex64")),
-            ("complex128", np.dtype("complex128")),
-            ("complex256", np.dtype("complex256")),
-            ("Complex64", np.dtype("complex128")),
-            ("Complex128", np.dtype("complex256")),
-            (np.dtype("complex64"), np.dtype("complex64")),
-            (np.dtype("complex128"), np.dtype("complex128")),
-            (np.dtype("complex256"), np.dtype("complex256")),
-            # Strings
-            (str, np.dtype("O")),
-            (bytes, np.dtype("O")),
-            ("str", np.dtype("O")),
-            ("bytes", np.dtype("O")),
-            ("U", np.dtype("O")),
-            ("object", np.dtype("O")),
-            ("bytes", np.dtype("O")),
-            (np.dtype("O"), np.dtype("O")),
-            # Datetime-like objects
-            ("M8[ns]", np.dtype("<M8[ns]")),
-            ("datetime64[ns]", np.dtype("<M8[ns]")),
-            (np.dtype("<M8[ns]"), np.dtype("<M8[ns]")),
-            ("m8[ns]", np.dtype("<m8[ns]")),
-            ("timedelta64[ns]", np.dtype("<m8[ns]")),
-            (np.dtype("<m8[ns]"), np.dtype("<m8[ns]")),
-            # Boolean
-            (bool, np.dtype("bool")),
-            ("bool", np.dtype("bool")),
-            (np.dtype("bool"), np.dtype("bool")),
-            # Categorical
-            ("category", CategoricalDtype(categories=[], ordered=False)),
-            (
-                CategoricalDtype(categories=[], ordered=False),
-                CategoricalDtype(categories=[], ordered=False),
-            ),
-        ],
+        "dtype",
+        tm.ALL_INT_DTYPES
+        + tm.ALL_EA_INT_DTYPES
+        + tm.FLOAT_DTYPES
+        + tm.COMPLEX_DTYPES
+        + tm.DATETIME64_DTYPES
+        + tm.TIMEDELTA64_DTYPES
+        + tm.BOOL_DTYPES,
+    )
+    def test_check_dtype_empty_numeric_column(self, dtype):
+        # GH24386: Ensure dtypes are set correctly for an empty DataFrame.
+        # Empty DataFrame is generated via dictionary data with non-overlapping columns.
+        data = pd.DataFrame({"a": [1, 2]}, columns=["b"], dtype=dtype)
+
+        assert data.b.dtype == dtype
+
+    @pytest.mark.parametrize(
+        "dtype", tm.STRING_DTYPES + tm.BYTES_DTYPES + tm.OBJECT_DTYPES
     )
-    def test_check_dtype_empty_column(self, input_value, expected_value):
+    def test_check_dtype_empty_string_column(self, dtype):
         # GH24386: Ensure dtypes are set correctly for an empty DataFrame.
         # Empty DataFrame is generated via dictionary data with non-overlapping columns.
-        data = pd.DataFrame({"a": [1, 2]}, columns=["b"], dtype=input_value)
-        assert data.b.dtype == expected_value
+        data = pd.DataFrame({"a": [1, 2]}, columns=["b"], dtype=dtype)
+
+        assert data.b.dtype.name == "object"
 
     def test_from_records_with_datetimes(self):