TST: Series construction from ExtensionDtype scalar

[arw2019]

• closes BUG: Constructing a Series from a scalar generally doesn't work for extension types #28401
• tests added / passed
• passes black pandas
• passes git diff upstream/master -u -- "*.py" | flake8 --diff
• whatsnew entry

[jbrockmendel]

this looks fine. should there be an analogous test in tests.extension?

[arw2019]

this looks fine. should there be an analogous test in tests.extension?

Hmmm do you mean something like this?

In [7]: pd.array(pd.Interval(0, 1))
(...)
ValueError: Cannot pass scalar '(0, 1]' to 'pandas.array'.

We test this here:

pandas/pandas/tests/arrays/test_array.py

Lines 287 to 290 in 52a1725

	def test_scalar_raises():
	with pytest.raises(ValueError, match="Cannot pass scalar '1'"):
	pd.array(1)

and

pandas/pandas/tests/arrays/floating/test_construction.py

Lines 85 to 108 in 52a1725

	@pytest.mark.parametrize(
	"values",
	[
	["foo", "bar"],
	["1", "2"],
	"foo",
	1,
	1.0,
	pd.date_range("20130101", periods=2),
	np.array(["foo"]),
	[[1, 2], [3, 4]],
	[np.nan, {"a": 1}],
	],
	)
	def test_to_array_error(values):
	# error in converting existing arrays to FloatingArray
	msg = (
	r"(:?.* cannot be converted to a FloatingDtype)"
	r"|(:?values must be a 1D list-like)"
	r"|(:?Cannot pass scalar)"
	)
	with pytest.raises((TypeError, ValueError), match=msg):
	pd.array(values, dtype="Float64")

[jreback]

can you create a fixture of the ea_scalars and use it here: https://github.com/pandas-dev/pandas/blob/master/pandas/tests/frame/test_constructors.py#L738 and in the new test you are adding

[jreback]

there are also similar tests for a dict of a scalar in both series/frame which could be updated to use the fixture as well

[arw2019]

can you create a fixture of the ea_scalars and use it here: https://github.com/pandas-dev/pandas/blob/master/pandas/tests/frame/test_constructors.py#L738 and in the new test you are adding

Done

[jreback]

there are also similar tests for a dict of a scalar in both series/frame which could be updated to use the fixture as well

[arw2019]

xref #38032 for a weird bug when the timedelta is in ns

[jreback]

great thanks. testing catching edge cases, who would think!

[jreback]

great thanks. testing catching edge cases, who would think!

[jreback]

thanks @arw2019

FYI there maybe other places where we can use this fixture, if its simple, would take a PR, if not, pls open an issue.

[arw2019]

FYI there maybe other places where we can use this fixture, if its simple, would take a PR, if not, pls open an issue.

Working on it. Probably will be a single PR but will see