BUG: DafaFrame.insert doesn't raise an exception when inserting another DataFrame

• I have checked that this issue has not already been reported.

• I have confirmed this bug exists on the latest version of pandas.

• (optional) I have confirmed this bug exists on the master branch of pandas.

---

Code Sample, a copy-pastable example

import pandas
df = pandas.DataFrame({'col1': [1, 2], 'col2': [3, 4]})
df.insert(1, "newcol", df)
df
   col1 newcol  col2
0     1   col1     3
1     2   col2     4

Problem description

Dataframe should take int, Series, or array-like as a value and throw an exception in case DataFrame is passed.

Expected Output

Behavior in 1.2.5

import pandas
df = pandas.DataFrame({'col1': [1, 2], 'col2': [3, 4]})
df.insert(1, "newcol", df)
ValueError: Wrong number of items passed 2, placement implies 1

Output of pd.show_versions()

pandas : 1.3.0 numpy : 1.20.3 pytz : 2020.1 dateutil : 2.8.1 pip : 21.1.2 setuptools : 49.6.0.post20210108 Cython : None pytest : 6.2.4 hypothesis : None sphinx : 4.0.2 blosc : None feather : 0.4.1 xlsxwriter : None lxml.etree : 4.6.3 html5lib : None pymysql : None psycopg2 : None jinja2 : 3.0.1 IPython : 7.24.1 pandas_datareader: None bs4 : 4.9.3 bottleneck : None fsspec : 2021.05.0 fastparquet : None gcsfs : None matplotlib : 3.2.2 numexpr : 2.7.3 odfpy : None openpyxl : 3.0.7 pandas_gbq : 0.15.0 pyarrow : 3.0.0 pyxlsb : None s3fs : None scipy : 1.6.3 sqlalchemy : 1.4.18 tables : 3.6.1 tabulate : None xarray : 0.18.2 xlrd : 2.0.1 xlwt : None numba : None

[jreback]

we should have an explicit test for this

[YarShev]

Feel free to close the issue because I see expected behavior of the operation to me since 1.3.1.