[1.8 backport] Unit test selection method (#10102)

[MichelleArk]

(cherry picked from commit 43d6c2f)

resolves #

Problem

Solution

Checklist

• I have read the contributing guide and understand what's expected of me
• I have run this code in development and it appears to resolve the stated issue
• This PR includes tests, or tests are not required/relevant for this PR
• This PR has no interface changes (e.g. macros, cli, logs, json artifacts, config files, adapter interface, etc) or this PR has already received feedback and approval from Product or DX
• This PR includes type annotations for new and modified functions

[codecov]

Codecov Report

Attention: Patch coverage is 88.23529% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 88.21%. Comparing base (8926c2c) to head (a7e567b).

Files	Patch %	Lines
core/dbt/graph/selector_methods.py	88.23%	2 Missing ⚠️

Additional details and impacted files

@@              Coverage Diff               @@
##           1.8.latest   #10109      +/-   ##
==============================================
+ Coverage       87.23%   88.21%   +0.97%     
==============================================
  Files             181      181              
  Lines           22733    22750      +17     
==============================================
+ Hits            19832    20069     +237     
+ Misses           2901     2681     -220     

Flag	Coverage Δ
integration	85.55% <17.64%> (+1.04%)	⬆️
unit	62.62% <88.23%> (+0.01%)	⬆️

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