chore(tests): improve test quality & tooling (Phase 4)

[SamyRai]

Phase 4: Improve Test Quality & Tooling (MEDIUM PRIORITY)

Priority: 🟡 MEDIUM - Quality improvements and modern tooling

Problem Statement

Missing modern testing patterns (2026 standards):

• ❌ No parameterized tests (rstest) - causes code duplication
• ❌ No test fixtures as function parameters
• ❌ No builder pattern for complex test data
• ❌ No snapshot testing for API contracts
• ❌ No nextest configuration for optimal parallelization

Test quality issues:

• Manual test data creation (verbose, error-prone)
• Duplicated assertion logic across tests
• No reusable test utilities
• Hardcoded test configuration (proptest: 1000 cases everywhere)

Goals

• ✅ Add rstest for parameterized testing (reduce duplication by 40%)
• ✅ Implement test data builders (fluent API)
• ✅ Add comprehensive assertions module
• ✅ Introduce insta snapshot tests for API stability
• ✅ Configure nextest for faster CI runs

Implementation Plan

1. Add rstest for parameterized tests:

   #[rstest]
   #[case(StorageClass::Hot, "hot_")]
   #[case(StorageClass::Cold, "cold_")]
   fn blob_path_prefix_matches_storage_class(
       #[case] class: StorageClass,
       #[case] expected_prefix: &str,
   ) {
       assert_eq!(blob.path_prefix(), expected_prefix);
   }

2. Implement test builders:

   let object = TestObjectBuilder::new()
       .namespace("media")
       .tenant_id(tenant_id)
       .with_metadata(metadata)
       .in_storage_class(StorageClass::Hot)
       .build();

3. Add comprehensive assertions module:

   // common/assertions.rs
   pub mod response {
       pub fn assert_ok_with_json(resp: Response, expected_keys: &[&str]);
       pub fn assert_error(resp: Response, status: StatusCode, error_type: &str);
   }
   
   pub mod domain {
       pub fn assert_object_committed(obj: &Object);
       pub fn assert_blob_matches(blob: &Blob, expected: &Blob);
   }

4. Add snapshot testing for API contracts:

   use insta::assert_json_snapshot;
   
   #[tokio::test]
   async fn openapi_spec_matches_snapshot() {
       let spec = get_openapi_spec().await;
       assert_json_snapshot!(spec);
   }

5. Configure nextest:

   # .config/nextest.toml
   [profile.default]
   retries = { backoff = "exponential", count = 2, delay = "1s" }
   slow-timeout = { period = "60s", terminate-after = 2 }
   threads = "num-cpus"
   
   [profile.ci]
   retries = { backoff = "exponential", count = 3, delay = "2s" }
   fail-fast = false

New Dependencies to Add

[dev-dependencies]
rstest = "0.23"                              # Parameterized tests
rstest_reuse = "0.8"                         # Reusable test templates
insta = { version = "1.40", features = ["json", "yaml"] }  # Snapshot testing
fake = { version = "2.9", features = ["derive"] }          # Fake data generators
tracing-test = "0.2"                         # Capture logs in tests
cargo-nextest = "0.9"                        # Faster test runner

Success Criteria

• ✅ All parameterizable tests converted to rstest
• ✅ Test builders reduce setup code by 50%
• ✅ Reusable assertions across all test suites
• ✅ OpenAPI spec has snapshot test
• ✅ Nextest runs full suite in <60s (vs 90s+ currently)
• ✅ All 293 tests still pass

Impact Metrics

Before:

• Test setup: ~20 lines per test (manual construction)
• Test runtime: ~90s full suite
• Parameterized tests: manual duplication

After:

• Test setup: ~5 lines per test (builders)
• Test runtime: <60s with nextest
• Parameterized tests: single rstest definition

Related PRs

• Depends on: Phase 3 (feature organization)
• Enables: Phase 5 (coverage expansion)

Estimated Effort: 2-3 days
ROI: 50% less test code, 30% faster CI, easier test authoring

Relates to #12
Addresses #13

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Part of #12
Fixes #13