GH1043 Update _typing.pyi: add "cross" option to JoinHow (pandas-dev#1044)

* Update _typing.pyi: add "cross" option to JoinHow

* Removed "cross" option from JoinHow and added it back to MergeHow

* Replaced JoinHow with MergeHow in frame.join

* Added a test for join "how"

* Update test_frame.py: used check(assert_type pattern in unit test

* Update test_frame.py

Fix formatting

Author: brzegorzTesco

pandas-stubs/core/frame.pyi

@@ -1503,7 +1503,7 @@ class DataFrame(NDFrame, OpsMixin):
         self,
         other: DataFrame | Series | list[DataFrame | Series],
         on: _str | list[_str] | None = ...,
-        how: JoinHow = ...,
+        how: MergeHow = ...,
         lsuffix: _str = ...,
         rsuffix: _str = ...,
         sort: _bool = ...,

tests/test_frame.py

@@ -2504,6 +2504,16 @@ def test_join() -> None:
     check(assert_type(left.join(right, validate="1:m"), pd.DataFrame), pd.DataFrame)
 
 
+def test_types_join() -> None:
+    df1 = pd.DataFrame({"A": [1, 2], "B": ["test", "test"]})
+    df2 = pd.DataFrame({"C": [2, 3], "D": ["test", "test"]})
+    check(assert_type(df1.join(df2, how="cross"), pd.DataFrame), pd.DataFrame)
+    check(assert_type(df1.join(df2, how="inner"), pd.DataFrame), pd.DataFrame)
+    check(assert_type(df1.join(df2, how="outer"), pd.DataFrame), pd.DataFrame)
+    check(assert_type(df1.join(df2, how="left"), pd.DataFrame), pd.DataFrame)
+    check(assert_type(df1.join(df2, how="right"), pd.DataFrame), pd.DataFrame)
+
+
 def test_types_ffill() -> None:
     # GH 44
     df = pd.DataFrame([[1, 2, 3]])