MBL-1017: Add features to CombineTestObserver

Kickstarter.xcodeproj/project.pbxproj

@@ -1487,6 +1487,7 @@
 		E10D06632ACF385E00470B5C /* FetchBackerProjectsQuery.json in Resources */ = {isa = PBXBuildFile; fileRef = E10D06622ACF385E00470B5C /* FetchBackerProjectsQuery.json */; };
 		E10D06652AD48C9C00470B5C /* FetchBackerProjectsQueryRequestForTests.graphql_test in Resources */ = {isa = PBXBuildFile; fileRef = E10D06642AD48C9C00470B5C /* FetchBackerProjectsQueryRequestForTests.graphql_test */; };
 		E170B9112B20E83B001BEDD7 /* MockGraphQLClient+CombineTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = E170B9102B20E83B001BEDD7 /* MockGraphQLClient+CombineTests.swift */; };
+		E1889D8F2B6065E1004FBE21 /* CombineTestObserverTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = E1889D8D2B6065D6004FBE21 /* CombineTestObserverTests.swift */; };
 		E1A1491E2ACDD76800F49709 /* FetchBackerProjectsQuery.graphql in Resources */ = {isa = PBXBuildFile; fileRef = E1A1491D2ACDD76700F49709 /* FetchBackerProjectsQuery.graphql */; };
 		E1A149202ACDD7BF00F49709 /* FetchProjectsEnvelope+FetchBackerProjectsQueryData.swift in Sources */ = {isa = PBXBuildFile; fileRef = E1A1491F2ACDD7BF00F49709 /* FetchProjectsEnvelope+FetchBackerProjectsQueryData.swift */; };
 		E1A149222ACE013100F49709 /* FetchProjectsEnvelope.swift in Sources */ = {isa = PBXBuildFile; fileRef = E1A149212ACE013100F49709 /* FetchProjectsEnvelope.swift */; };
@@ -3058,6 +3059,7 @@
 		E10D06622ACF385E00470B5C /* FetchBackerProjectsQuery.json */ = {isa = PBXFileReference; lastKnownFileType = text.json; path = FetchBackerProjectsQuery.json; sourceTree = "<group>"; };
 		E10D06642AD48C9C00470B5C /* FetchBackerProjectsQueryRequestForTests.graphql_test */ = {isa = PBXFileReference; lastKnownFileType = text; path = FetchBackerProjectsQueryRequestForTests.graphql_test; sourceTree = "<group>"; };
 		E170B9102B20E83B001BEDD7 /* MockGraphQLClient+CombineTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = "MockGraphQLClient+CombineTests.swift"; sourceTree = "<group>"; };
+		E1889D8D2B6065D6004FBE21 /* CombineTestObserverTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = CombineTestObserverTests.swift; sourceTree = "<group>"; };
 		E1A1491D2ACDD76700F49709 /* FetchBackerProjectsQuery.graphql */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = text; path = FetchBackerProjectsQuery.graphql; sourceTree = "<group>"; };
 		E1A1491F2ACDD7BF00F49709 /* FetchProjectsEnvelope+FetchBackerProjectsQueryData.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = "FetchProjectsEnvelope+FetchBackerProjectsQueryData.swift"; sourceTree = "<group>"; };
 		E1A149212ACE013100F49709 /* FetchProjectsEnvelope.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = FetchProjectsEnvelope.swift; sourceTree = "<group>"; };
@@ -6875,6 +6877,7 @@
 			children = (
 				E1EA34EE2AE1B28400942A04 /* Signal+Combine.swift */,
 				E1FDB1E72AEAAC6100285F93 /* CombineTestObserver.swift */,
+				E1889D8D2B6065D6004FBE21 /* CombineTestObserverTests.swift */,
 			);
 			path = combine;
 			sourceTree = "<group>";
@@ -8637,6 +8640,7 @@
 				D755ECA92319AF4D0096F189 /* CreateBackingEnvelope.swift in Sources */,
 				D0158A131EEB30A2006E7684 /* DiscoveryEnvelopeTemplates.swift in Sources */,
 				06232D452795EC4600A81755 /* TextViewElement.swift in Sources */,
+				E1889D8F2B6065E1004FBE21 /* CombineTestObserverTests.swift in Sources */,
 				D01588431EEB2ED7006E7684 /* Activity.swift in Sources */,
 				8ACF36F7262763960026E74D /* MockPerimeterXTypes.swift in Sources */,
 				D01588CD1EEB2ED7006E7684 /* ShippingRulesEnvelopeLenses.swift in Sources */,

KsApi/combine/CombineTestObserver.swift

@@ -1,7 +1,13 @@
 import Combine
 import Foundation
+import XCTest
 
+/**
+ A wrapper around a subscription that saves all events to a public array so
+ that assertions can be made on a publisher's behavior.
+ */
 public final class CombineTestObserver<Value, Error: Swift.Error> {
+  /// Represents the state of an event in the publisher's timeline
   public enum Event {
     case value(Value)
     case error(Error)
@@ -27,4 +33,161 @@ public final class CombineTestObserver<Value, Error: Swift.Error> {
     }
     .store(in: &self.subscriptions)
   }
+
+  /// Get all of the next values emitted by the signal.
+  public var values: [Value] {
+    var values: [Value] = []
+    for event in self.events {
+      switch event {
+      case let .value(v):
+        values.append(v)
+      default: break
+        // do nothing
+      }
+    }
+
+    return values
+  }
+
+  /// Get the last value emitted by the signal.
+  public var lastValue: Value? {
+    return self.values.last
+  }
+
+  /// `true` if at least one `.Next` value has been emitted.
+  public var didEmitValue: Bool {
+    return self.values.count > 0
+  }
+
+  /// The failed error if the signal has failed.
+  public var failedError: Error? {
+    var errors: [Error] = []
+    for event in self.events {
+      switch event {
+      case let .error(e):
+        errors.append(e)
+      default: break
+        // do nothing
+      }
+    }
+
+    assert(
+      errors.count <= 1,
+      "I'm pretty sure a Combine publisher can only ever emit one error. If this fails, I've learned something new today."
+    )
+
+    return errors.last
+  }
+
+  /// `true` if a `.Failed` event has been emitted.
+  public var didFail: Bool {
+    return self.failedError != nil
+  }
+
+  /// `true` if a `.Finished` event has been emitted or a `.Failed` event has been ommitted
+  public var didComplete: Bool {
+    return self.events.contains { event in
+      switch event {
+      case .finished:
+        return true
+      case .error:
+        return true
+
+      default: break
+      }
+      return false
+    }
+  }
+
+  public func assertDidComplete(_ message: String = "Should have completed.",
+                                file: StaticString = #file, line: UInt = #line) {
+    XCTAssertTrue(self.didComplete, message, file: file, line: line)
+  }
+
+  public func assertDidFail(_ message: String = "Should have failed.",
+                            file: StaticString = #file, line: UInt = #line) {
+    XCTAssertTrue(self.didFail, message, file: file, line: line)
+  }
+
+  public func assertDidNotFail(_ message: String = "Should not have failed.",
+                               file: StaticString = #file, line: UInt = #line) {
+    XCTAssertFalse(self.didFail, message, file: file, line: line)
+  }
+
+  public func assertDidNotComplete(_ message: String = "Should not have completed",
+                                   file: StaticString = #file, line: UInt = #line) {
+    XCTAssertFalse(self.didComplete, message, file: file, line: line)
+  }
+
+  public func assertDidEmitValue(_ message: String = "Should have emitted at least one value.",
+                                 file: StaticString = #file, line: UInt = #line) {
+    XCTAssert(self.values.count > 0, message, file: file, line: line)
+  }
+
+  public func assertDidNotEmitValue(_ message: String = "Should not have emitted any values.",
+                                    file: StaticString = #file, line: UInt = #line) {
+    XCTAssertEqual(0, self.values.count, message, file: file, line: line)
+  }
+
+  public func assertDidTerminate(
+    _ message: String = "Should have terminated, i.e. completed/failed/interrupted.",
+    file: StaticString = #file, line: UInt = #line
+  ) {
+    XCTAssertTrue(self.didFail || self.didComplete, message, file: file, line: line)
+  }
+
+  public func assertDidNotTerminate(
+    _ message: String = "Should not have terminated, i.e. completed/failed/interrupted.",
+    file: StaticString = #file, line: UInt = #line
+  ) {
+    XCTAssertTrue(!self.didFail && !self.didComplete, message, file: file, line: line)
+  }
+
+  public func assertValueCount(_ count: Int, _ message: String? = nil,
+                               file: StaticString = #file, line: UInt = #line) {
+    XCTAssertEqual(
+      count,
+      self.values.count,
+      message ?? "Should have emitted \(count) values",
+      file: file,
+      line: line
+    )
+  }
+}
+
+extension CombineTestObserver where Value: Equatable {
+  public func assertValue(_ value: Value, _ message: String? = nil,
+                          file: StaticString = #file, line: UInt = #line) {
+    XCTAssertEqual(1, self.values.count, "A single item should have been emitted.", file: file, line: line)
+    XCTAssertEqual(
+      value,
+      self.lastValue,
+      message ?? "A single value of \(value) should have been emitted",
+      file: file,
+      line: line
+    )
+  }
+
+  public func assertLastValue(_ value: Value, _ message: String? = nil,
+                              file: StaticString = #file, line: UInt = #line) {
+    XCTAssertEqual(
+      value,
+      self.lastValue,
+      message ?? "Last emitted value is equal to \(value).",
+      file: file,
+      line: line
+    )
+  }
+
+  public func assertValues(_ values: [Value], _ message: String = "",
+                           file: StaticString = #file, line: UInt = #line) {
+    XCTAssertEqual(values, self.values, message, file: file, line: line)
+  }
+}
+
+extension CombineTestObserver where Error: Equatable {
+  public func assertFailed(_ expectedError: Error, message: String = "",
+                           file: StaticString = #file, line: UInt = #line) {
+    XCTAssertEqual(expectedError, self.failedError, message, file: file, line: line)
+  }
 }

KsApi/combine/CombineTestObserverTests.swift

@@ -0,0 +1,64 @@
+import Combine
+import XCTest
+
+final class ConcreteError: Error {
+  var message: String
+
+  init(message: String) {
+    self.message = message
+  }
+}
+
+final class CombineTestObserverTests: XCTestCase {
+  var publisher = PassthroughSubject<Bool, ConcreteError>()
+  var observer = CombineTestObserver<Bool, ConcreteError>()
+
+  override func setUp() {
+    self.publisher = PassthroughSubject<Bool, ConcreteError>()
+    self.observer = CombineTestObserver<Bool, ConcreteError>()
+
+    self.observer.observe(self.publisher)
+  }
+
+  func testValues() {
+    self.publisher.send(true)
+    self.observer.assertValue(true)
+    self.observer.assertDidEmitValue()
+
+    self.publisher.send(false)
+    self.observer.assertLastValue(false)
+
+    self.observer.assertValues([true, false])
+    self.observer.assertValueCount(2)
+
+    self.observer.assertDidNotFail()
+    self.observer.assertDidNotComplete()
+    self.observer.assertDidNotTerminate()
+  }
+
+  func testFailure() {
+    self.publisher.send(true)
+    self.observer.assertValue(true)
+
+    let msg = "failure :("
+    let error = ConcreteError(message: msg)
+
+    publisher.send(completion: Subscribers.Completion.failure(error))
+
+    self.observer.assertDidFail()
+    XCTAssertEqual(self.observer.failedError?.message, msg)
+
+    // n.B. in Combine, a publisher also finishes and cannot continue
+    // after an error occurs.
+    self.observer.assertDidComplete()
+  }
+
+  func testCompletion() {
+    self.publisher.send(false)
+    self.observer.assertValue(false)
+
+    self.publisher.send(completion: Subscribers.Completion.finished)
+    self.observer.assertDidComplete()
+    self.observer.assertDidNotFail()
+  }
+}