docs: add comprehensive rustdoc for testing module #372

Job	Run time
Minimum Supported Rust Version	1m 0s
Dependency Management	15s
Docker Integration Tests	4m 21s
Test Suite (ubuntu-latest, beta)	2m 16s
Security Audit	17s
Documentation	43s
Test Suite (windows-latest, stable)	7m 11s
Test Suite (macos-latest, stable)	2m 31s
Test Suite (ubuntu-latest, stable)	2m 22s
	20m 56s

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