`test_regr_funcs` does not test `datafusion-python` functions

[Michael-J-Ward]

test_regr_funcs in test_functions.py uses a ctx.sql(query) statement, which bypasses the datafusion-python functions it should be testing.

datafusion-python/python/datafusion/tests/test_functions.py

Lines 834 to 853 in fd6b4df

	def test_regr_funcs(df):
	# test case base on
	# https://github.com/apache/arrow-datafusion/blob/d1361d56b9a9e0c165d3d71a8df6795d2a5f51dd/datafusion/core/tests/sqllogictests/test_files/aggregate.slt#L2330
	ctx = SessionContext()
	result = ctx.sql(
	"select regr_slope(1,1), regr_intercept(1,1), "
	"regr_count(1,1), regr_r2(1,1), regr_avgx(1,1), "
	"regr_avgy(1,1), regr_sxx(1,1), regr_syy(1,1), "
	"regr_sxy(1,1);"
	).collect()
	assert result[0].column(0) == pa.array([None], type=pa.float64())
	assert result[0].column(1) == pa.array([None], type=pa.float64())
	assert result[0].column(2) == pa.array([1], type=pa.float64())
	assert result[0].column(3) == pa.array([None], type=pa.float64())
	assert result[0].column(4) == pa.array([1], type=pa.float64())
	assert result[0].column(5) == pa.array([1], type=pa.float64())
	assert result[0].column(6) == pa.array([0], type=pa.float64())
	assert result[0].column(7) == pa.array([0], type=pa.float64())
	assert result[0].column(8) == pa.array([0], type=pa.float64())