Columns and DataType Not Explicitly Set on line 35 of test_directed_node_generator.py

[CodeSmileBot]

Hello!

I found an AI-Specific Code smell in your project.
The smell is called: Columns and DataType Not Explicitly Set

You can find more information about it in this paper: https://dl.acm.org/doi/abs/10.1145/3522664.3528620.

According to the paper, the smell is described as follows:

Problem	If the columns are not selected explicitly, it is not easy for developers to know what to expect in the downstream data schema. If the datatype is not set explicitly, it may silently continue the next step even though the input is unexpected, which may cause errors later. The same applies to other data importing scenarios.
Solution	It is recommended to set the columns and DataType explicitly in data processing.
Impact	Readability

Example:

### Pandas Column Selection
import pandas as pd
df = pd.read_csv('data.csv')
+ df = df[['col1', 'col2', 'col3']]

### Pandas Set DataType
import pandas as pd
- df = pd.read_csv('data.csv')
+ df = pd.read_csv('data.csv', dtype={'col1': 'str', 'col2': 'int', 'col3': 'float'})

You can find the code related to this smell in this link:

stellargraph/tests/mapper/test_directed_node_generator.py

Lines 25 to 45 in 84336e1

	# FIXME (#535): Consider using graph fixtures
	def create_simple_graph():
	"""
	Creates a simple directed graph for testing. The node ids are integers.
	Returns:
	A small, directed graph with 3 nodes and 2 edges in StellarDiGraph format.
	"""
	nodes = pd.DataFrame([-1, -2, -3], index=[1, 2, 3])
	edges = pd.DataFrame([(1, 2), (2, 3)], columns=["source", "target"])
	return StellarDiGraph(nodes, edges)
	class TestDirectedNodeGenerator(object):
	"""
	Test various aspects of the directed GrapohSAGE node generator, with the focus
	on the sampled neighbourhoods and the extracted features.
	"""
	def sample_one_hop(self, num_in_samples, num_out_samples):

.

I also found instances of this smell in other files, such as:

File: https://github.com/stellargraph/stellargraph/blob/master/demos/community_detection/utils.py#L212-L222 Line: 217
File: https://github.com/stellargraph/stellargraph/blob/master/demos/community_detection/utils.py#L235-L245 Line: 240
File: https://github.com/stellargraph/stellargraph/blob/master/stellargraph/core/convert.py#L379-L389 Line: 384
File: https://github.com/stellargraph/stellargraph/blob/master/stellargraph/core/convert.py#L464-L474 Line: 469
File: https://github.com/stellargraph/stellargraph/blob/master/stellargraph/core/convert.py#L379-L389 Line: 384
.

I hope this information is helpful!