🌱 Refactor CronJob controller tests: utils extraction, env isolation for easier test scenario extension

[rayowang]

…structure optimization

Fixes #4140

Refactor CronJob controller tests by extracting reusable utility functions, isolating test environments via unique namespaces and lifecycle hooks, and optimizing test structure (splitting monolithic cases, unifying timeout/interval params, aligning with Kubebuilder best practices). These improvements streamline test maintenance and lay a clear, scalable foundation for easily adding more test scenarios (e.g., edge cases, feature-specific tests) in subsequent iterations, while fully preserving the original core test logic and functionality.

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[Copilot]

Pull Request Overview

This PR refactors the CronJob controller tests to improve maintainability and support easier extension of test scenarios. It extracts reusable utility functions for common test operations, implements per-test namespace isolation to prevent test interference, and restructures the monolithic test case into focused, independently executable tests.

Key changes include:

• Extraction of helper functions (assertCondition, randomString, createTestCronJob, createOwnedJob) to reduce code duplication
• Implementation of unique namespace generation and BeforeEach/AfterEach lifecycle hooks for test isolation
• Restructuring from a single large test case into smaller, focused Context blocks

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[camilamacedo86]

The code under book/src contains sample files used in the tutorials.
All content within /* ... */ blocks represents text used for the documentation. Cannot be removed, you can see the preview of the docs with the ci:

The goal here of those tutorials are to ensure the test structure remains as similar as possible to what we scaffold for the deploy image.
You can refer to this example for reference:

https://github.com/kubernetes-sigs/kubebuilder/blob/master/testdata/project-v4-with-plugins/internal/controller/busybox_controller_test.go

However, in this case, we’ll need to adapt it to use a CronJob instead of BusyBox.

Additionally, note that the files under this path are auto-generated via make generate-docs.

Therefore, any required modifications should be made in the hack/generate scripts.
For more context, see this related discussion: #5024