Replace integration tests with mocked URLSession tests

[leogdion]

⚠️ Potential issue | 🟠 Major

Replace integration tests with mocked URLSession tests.

These integration tests have several reliability and maintainability concerns:

1. External dependencies: Tests rely on external services (apple.com, httpbin.org) which can fail, timeout, or change behavior
2. Flakiness: Network issues, service outages, or rate limiting will cause non-deterministic test failures
3. CI/CD impact: Tests will fail in offline, sandboxed, or network-restricted environments
4. Performance: Network calls significantly slow down test execution
5. Weak assertions (lines 50, 71): Using _ = lastModified doesn't validate behavior

As per coding guidelines: "Use mock objects from BushelTestUtilities for testing protocol conformances and creating test doubles."

Recommended approach: Mock URLSession using protocol-based design

Create a protocol for URLSession operations in BushelUtilities:

public protocol URLSessionProtocol {
  func data(from url: URL) async throws -> (Data, URLResponse)
  func data(for request: URLRequest) async throws -> (Data, URLResponse)
}

extension URLSession: URLSessionProtocol {}

Then add mocks in BushelTestUtilities and test with controlled responses.

Would you like me to help implement this mocking infrastructure?

🤖 Prompt for AI Agents

In @Tests/BushelUtlitiesTests/URLSessionTests.swift around lines 38-107, The
tests in URLSessionTests (methods testFetchLastModifiedWithValidURL,
testFetchLastModifiedWithInvalidURL, testFetchLastModifiedReturnsNilGracefully,
testFetchDataWithValidURL, testFetchDataWithoutLastModifiedTracking,
testFetchDataWithInvalidURLThrows) are integration tests hitting real networks;
replace them with deterministic unit tests using a URLSessionProtocol and mocks
from BushelTestUtilities. Add a URLSessionProtocol (methods data(from:) and
data(for:)), extend URLSession to conform, create a MockURLSession in
BushelTestUtilities that returns controlled (Data, URLResponse) or throws,
update the code under test to accept a URLSessionProtocol (or provide an
injectable session on URLSession.shared wrappers like fetchLastModified and
fetchData), rewrite each test to inject the mock responses (including a
404/timeout/error case) and replace `_ = lastModified` with concrete assertions
(e.g., XCTAssertEqual/ XCTAssertNil against the mocked Last-Modified header or
data content).

Originally posted by @coderabbitai[bot] in #126 (comment)