fix(#11963): Migrate StudyViewControllerTest to JUnit 5 and fix ignored tests

[purvanshjoshi]

Fix #11963

Describe changes proposed in this pull request:

• Migrated StudyViewControllerTest.java from JUnit 4 to JUnit 5, updating annotations (@ExtendWith, @BeforeEach, @Disabled) and imports.
• Fixed and enabled fetchClinicalDataBinCounts test:
  • Replaced mocked ClinicalDataBinUtil and ClinicalDataFetcher with real bean instances to verify actual binning logic.
  • Added IdPopulator to the test context to support the real ClinicalDataBinUtil.
  • Mocked CustomDataService to resolve dependency issues.
• Fixed and enabled fetchClinicalDataDensityPlot test:
  • Updated test assertions to match the API's sparse response format (verifying only populated bins instead of expecting a dense matrix).
  • Resolved a 403 Forbidden error by adding .with(csrf()) to the mock request builder.
• Verified all 19 tests in StudyViewControllerTest pass successfully.

Checks

• The commit log is comprehensible. It follows 7 rules of great commit messages. We can fix this during merge by using a squash+merge if necessary
• Has tests or has a separate issue that describes the types of test that should be created. If no test is included it should explicitly be mentioned in the PR why there is no test.
• Is this PR adding logic based on one or more clinical attributes? If yes, please make sure validation for this attribute is also present in the data validation / data loading layers (in backend repo) and documented in File-Formats Clinical data section!
• Make sure your PR has one of the labels defined in https://github.com/cBioPortal/cbioportal/blob/master/.github/release-drafter.yml

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[Copilot]

Pull request overview

This PR migrates StudyViewControllerTest from JUnit 4 to JUnit 5 and fixes two previously ignored tests (fetchClinicalDataBinCounts and fetchClinicalDataDensityPlot) that were failing due to incorrect mocking strategies and outdated assertions.

Changes:

• Migrated test class from JUnit 4 to JUnit 5 by updating annotations and imports
• Fixed fetchClinicalDataBinCounts test by replacing mocked ClinicalDataBinUtil and ClinicalDataFetcher with real bean instances, and adding required dependencies (IdPopulator, CustomDataService)
• Fixed fetchClinicalDataDensityPlot test by updating assertions to match the API's sparse response format (which filters out empty bins) and adding CSRF token to resolve 403 Forbidden error

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