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OR-5276 Debugging:: Printing events (#130)
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CombineDemo/CombineDemoTests/Debugging/PrintingEventsTests.swift
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| @@ -0,0 +1,95 @@ | ||
| // | ||
| // PrintingEventsTests.swift | ||
| // CombineDemoTests | ||
| // | ||
| // Created by Manish Rathi on 13/08/2023. | ||
| // | ||
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| import Foundation | ||
| import Combine | ||
| import XCTest | ||
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| /* | ||
| - Understanding the event flow in asynchronous programs has always been a challenge. | ||
| - It is particularly the case in the context of Combine, as chains of operators in a publisher may not all emit events at the same time. | ||
| - Combine provides a few operators to help with debugging your reactive flows. Knowing them will help you troubleshoot puzzling situations. | ||
| - `print(_:to:)` Prints log messages for all publishing events. | ||
| - https://developer.apple.com/documentation/combine/publisher/print(_:to:) | ||
| */ | ||
| final class PrintingEventsTests: XCTestCase { | ||
| var cancellables: Set<AnyCancellable>! | ||
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| override func setUp() { | ||
| super.setUp() | ||
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| cancellables = [] | ||
| } | ||
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| override func tearDown() { | ||
| cancellables = nil | ||
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| super.tearDown() | ||
| } | ||
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| func testPrintOperator() { | ||
| let publisher = (1...3).publisher | ||
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| publisher | ||
| .print("Logged a debug message") // This is magical operator for debug (using prefix in logging-message) | ||
| .sink { _ in } | ||
| .store(in: &cancellables) | ||
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| /* | ||
| // Prints: | ||
| // Logged a debug message: receive subscription: (1...3) | ||
| // Logged a debug message: request unlimited | ||
| // Logged a debug message: receive value: (1) | ||
| // Logged a debug message: receive value: (2) | ||
| // Logged a debug message: receive value: (3) | ||
| // Logged a debug message: receive finished | ||
| */ | ||
| } | ||
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| func testPrintOperatorWithTextOutputStream() { | ||
| let publisher = (1...3).publisher | ||
| let debugLogger = TimeStampDebugLogger() | ||
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| publisher | ||
| .print("Logged a debug message", to: debugLogger) // Using prefix with custom TimeStamp debugger for print | ||
| .sink { _ in } | ||
| .store(in: &cancellables) | ||
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| /* | ||
| // Prints: | ||
| // +0.00010s: Logged a debug message: receive subscription: (1...3) | ||
| // +0.00003s: Logged a debug message: request unlimited | ||
| // +0.00001s: Logged a debug message: receive value: (1) | ||
| // +0.00001s: Logged a debug message: receive value: (2) | ||
| // +0.00001s: Logged a debug message: receive value: (3) | ||
| // +0.00001s: Logged a debug message: receive finished | ||
| */ | ||
| } | ||
| } | ||
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| class TimeStampDebugLogger: TextOutputStream { | ||
| private var previousDate = Date() | ||
| private let formatter = NumberFormatter() | ||
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| init() { | ||
| formatter.maximumFractionDigits = 5 | ||
| formatter.minimumFractionDigits = 5 | ||
| } | ||
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| func write(_ string: String) { | ||
| let trimmedString = string.trimmingCharacters(in: .whitespacesAndNewlines) | ||
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| guard !trimmedString.isEmpty else { return } | ||
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| let nowDate = Date() | ||
| let formattedDate = formatter.string(for: nowDate.timeIntervalSince(previousDate))! | ||
| print("+\(formattedDate)s: \(trimmedString)") | ||
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| previousDate = nowDate | ||
| } | ||
| } |
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