Platform-agnostic concepts: shared/mobile/testing-concepts.md

Testing — Couchbase Lite iOS/macOS

Core principle: use a real in-memory database

CBL has no mock — use a real database in a temporary directory. It's fast (< 5ms to open) and gives accurate behaviour.

func tempDatabase() throws -> Database {
    let dir = FileManager.default.temporaryDirectory
        .appendingPathComponent(UUID().uuidString)
    try FileManager.default.createDirectory(at: dir, withIntermediateDirectories: true)
    var config = DatabaseConfiguration()
    config.directory = dir.path
    return try Database(name: "test", config: config)
}