Improve test coverage from 67% to 94%

[devin-ai-integration]

Summary

Adds JaCoCo coverage plugin and comprehensive unit/integration tests to increase instruction coverage from 67% → 94%.

New tests added (11 files):

• Service tests: QuoteServiceTest, ExperimentalRankingServiceTest, ProviderServiceTest
• Web controller tests: QuoteWebControllerTest, AdminControllerTest, ProviderWebControllerTest, HomeControllerTest
• API controller tests: ProviderApiControllerTest, MapApiControllerTest, HealthControllerTest
• Integration test: DataSeederTest

Key changes to pom.xml:

• Added JaCoCo Maven plugin with prepare-agent and report goals

Review & Testing Checklist for Human

Low risk — only adds tests and a coverage plugin; no source code changes.

• Run cd backend && ./mvnw test -q and confirm all 82+ tests pass with 0 failures
• Check JaCoCo report at backend/target/site/jacoco/index.html shows ≥85% instruction coverage

Notes

• Tests use MockMvc for controller tests, Mockito for service tests, and @SpringBootTest for integration tests
• UK postcode validation tests use valid format postcodes (e.g., "SW1A 1AA")

Link to Devin session: https://bobby-demo.devinenterprise.com/sessions/a91b9e60b18f4fc0b3b784e65b059883
Requested by: @bnob-git

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[devin-ai-integration]

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[devin-ai-integration]

Devin Review found 1 potential issue.

View 3 additional findings in Devin Review.

[devin-ai-integration]

🟡 Mockito stub for toDtoList never matches due to Provider lacking equals()

The mock at line 37 uses List.of(new Provider()) as the expected argument, but providerService.getAllProviders() (stubbed at line 36) returns a list containing a different new Provider() instance. Since Provider does not override equals() (backend/src/main/java/com/compare/domain/Provider.java), Mockito's default equals-based matching compares by reference identity, so the toDtoList stub never matches. The mock returns null instead of List.of(dto), and the test only passes because it asserts status().isOk() — ResponseEntity.ok(null) still returns HTTP 200. The test gives false confidence that the mapper integration is working.

Suggested change

	when(providerService.getAllProviders()).thenReturn(List.of(new Provider()));
	when(providerMapper.toDtoList(List.of(new Provider()))).thenReturn(List.of(dto));
	Provider provider = new Provider();
	when(providerService.getAllProviders()).thenReturn(List.of(provider));
	when(providerMapper.toDtoList(List.of(provider))).thenReturn(List.of(dto));

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