InjectableLoggers

A nice set of protocols that will help logger(s) at being loosely coupled, injectable and testable.

Example

To see the example project, run the following in your terminal:

pod try InjectableLoggers

Setup

Just add:

import InjectableLoggers

to the files where you need some injectable logging action.

Making your logger injectable

Depending on how much functionality you want (to expose) from a logger, make a logger conform to one of the following protocols:

CanLog

CanLogMessage

CanLogMessageAtLevel

All of thes protocols have lightweight and sensible default implementations and make sure you never have to implement more than one of their methods.

Making an existing logger injectable

When it uses instance methods for logging

extension SomeoneElsesLogger: CanLogMessageAtLevel /* CanLog || CanLogMessage */ {

    func log(_ message Any, at: LogLevel) {
        //call existing logging functionality here
    }
}

When it uses class methods for logging

struct Logger: CanLogMessageAtLevel /* CanLog || CanLogMessage */ {

    func log(_ message Any, at: LogLevel) {
        //call existing logging functionality here
    }
}

Doing some logging

Depending on which protocols your loggers conform to, you can call the following methods:

logger.log() //Will log "" to default LogLevel if expected
logger.log(42) //Will log 42 to default LogLevel if expected
logger.log("Something not to important", at LogLevel.verbose)
logger.log("Something broke!", at: LogLevel.error)

Bonus! This lib comes with two concrete loggers 🎉

ConsoleLogger

let logger: CanLogMessage = ConsoleLogger()

logger.log() // logs to console: ""
logger.log(42) // logs to console: 42
logger.log("Hi there") // logs to console: "Hi there"

Logger

let logger: CanLogMessageAtLevel = Logger(settings: .warningSettings)

logger.log("Some info", atLevel LogLevel.info) //Won't log anything because of settings
logger.log("Something's up") // logs to settings.destination: "⚠️ Something's up"
logger.log("Something went wrong") // logs to settings.destination: "⛔️ Something's up"

settings.destination?

Yes, settings has it’s own CanLogMessage instance (ConsoleLogger by default) which is used for logging all created strings. This not only made Logger completely testable (and tested) but it also allows you to log to different destinations if needed.

Testing that what was expected is being logged

Another bonus! This lib comes with a pretty handy mock logger called MockLogger 🎉

class ViewControllerTests: XCTestCase {
    
    var sut: ViewController!
    var mockLogger: MockLogger!
    
    override func setUp() {
        super.setUp()
        
        sut = ViewController()
        mockLogger = MockLogger()
    }
    
    // MARK: Single line assertions
    func testViewDidLoad() {
        //Arrange
        sut.logger = mockLogger //Inject mockLogger
        
        //Act
        sut.viewDidLoad()
        
        //Assert
        XCTAssertEqual(mockLogger.loggedMessages(at: Loglevel.info).last?.message as? String, "viewDidLoad()")
    }
    
    // MARK: More verbose assertions
    func testDidReceiveMemoryWarning() {
        //Arrange
        sut.logger = mockLogger //Inject mockLogger
        
        //Act
        sut.didReceiveMemoryWarning()
        
        //Assert
        XCTAssertEqual(mockLogger.loggedMessages.last?.message as? String, "didReceiveMemoryWarning()")
        XCTAssertEqual(mockLogger.loggedMessages.last?.level, Loglevel.warning)
    }
}

For some more advance testing check out the example project.

Installation

InjectableLoggers is available through Swift Package Manager. To install it, simply add it to your project using this repository’s URL as explained here.

License

InjectableLoggers is available under the MIT license. See the LICENSE file for more info.