Make XCTMain test observations configurable

Sources/XCTest/Public/XCTestMain.swift

@@ -62,7 +62,16 @@
 public func XCTMain(_ testCases: [XCTestCaseEntry]) -> Never {
     XCTMain(testCases, arguments: CommandLine.arguments)
 }
+
 public func XCTMain(_ testCases: [XCTestCaseEntry], arguments: [String]) -> Never {
+    XCTMain(testCases, arguments: arguments, observers: [PrintObserver()])
+}
+
+public func XCTMain(
+    _ testCases: [XCTestCaseEntry],
+    arguments: [String],
+    observers: [XCTestObservation]
+) -> Never {
     let testBundle = Bundle.main
 
     let executionMode = ArgumentParser(arguments: arguments).executionMode
@@ -128,7 +137,9 @@ public func XCTMain(_ testCases: [XCTestCaseEntry], arguments: [String]) -> Neve
     case .run(selectedTestNames: _):
         // Add a test observer that prints test progress to stdout.
         let observationCenter = XCTestObservationCenter.shared
-        observationCenter.addTestObserver(PrintObserver())
+        for observer in observers {
+            observationCenter.addTestObserver(observer)
+        }
 
         observationCenter.testBundleWillStart(testBundle)
         rootTestSuite.run()

Tests/Functional/Observation/MultipleObservers/main.swift

@@ -0,0 +1,138 @@
+// RUN: %{swiftc} %s -o %T/MultipleObservers
+// RUN: %T/MultipleObservers > %t || true
+// RUN: %{xctest_checker} %t %s
+
+#if os(macOS)
+    import SwiftXCTest
+#else
+    import XCTest
+#endif
+
+class Observer: XCTestObservation {
+    var startedBundlePaths = [String]()
+    var startedTestSuites = [XCTestSuite]()
+    var startedTestCaseNames = [String]()
+    var failureDescriptions = [String]()
+    var finishedTestCaseNames = [String]()
+    var finishedTestSuites = [XCTestSuite]()
+    var finishedBundlePaths = [String]()
+
+    func testBundleWillStart(_ testBundle: Bundle) {
+        startedBundlePaths.append(testBundle.bundlePath)
+    }
+
+    func testSuiteWillStart(_ testSuite: XCTestSuite) {
+        startedTestSuites.append(testSuite)
+    }
+
+    func testCaseWillStart(_ testCase: XCTestCase) {
+        startedTestCaseNames.append(testCase.name)
+    }
+
+    func testCase(_ testCase: XCTestCase, didFailWithDescription description: String, inFile filePath: String?, atLine lineNumber: Int) {
+        failureDescriptions.append(description)
+    }
+
+    func testCaseDidFinish(_ testCase: XCTestCase) {
+        finishedTestCaseNames.append(testCase.name)
+    }
+
+    func testSuiteDidFinish(_ testSuite: XCTestSuite) {
+        print("In \(#function): \(testSuite.name)")
+    }
+
+    func testBundleDidFinish(_ testBundle: Bundle) {
+        print("In \(#function)")
+    }
+}
+
+let observer1 = Observer()
+let observer2 = Observer()
+
+class Observation: XCTestCase {
+    static var allTests = {
+        return [
+            ("test_one", test_one),
+            ("test_two", test_two),
+            ("test_three", test_three),
+        ]
+    }()
+
+    func test_one() {
+        XCTAssertEqual(observer1.startedBundlePaths.count, 1)
+        XCTAssertEqual(observer2.startedBundlePaths.count, 1)
+        XCTAssertEqual(
+            observer1.startedTestSuites.count, 3,
+            "Three test suites should have started: 'All tests', 'tmp.xctest', and 'Observation'.")
+        XCTAssertEqual(
+            observer2.startedTestSuites.count, 3,
+            "Three test suites should have started: 'All tests', 'tmp.xctest', and 'Observation'.")
+        XCTAssertEqual(observer1.startedTestCaseNames, ["Observation.test_one"])
+        XCTAssertEqual(observer2.startedTestCaseNames, ["Observation.test_one"])
+        XCTAssertEqual(observer1.failureDescriptions, [])
+        XCTAssertEqual(observer2.failureDescriptions, [])
+        XCTAssertEqual(observer1.finishedTestCaseNames, [])
+        XCTAssertEqual(observer2.finishedTestCaseNames, [])
+        XCTAssertEqual(observer1.finishedBundlePaths.count, 0)
+        XCTAssertEqual(observer2.finishedBundlePaths.count, 0)
+
+        XCTFail("fail!")
+        XCTAssertEqual(observer1.failureDescriptions, ["failed - fail!"])
+        XCTAssertEqual(observer2.failureDescriptions, ["failed - fail!"])
+    }
+
+    func test_two() {
+        XCTAssertEqual(observer1.startedBundlePaths.count, 1)
+        XCTAssertEqual(observer2.startedBundlePaths.count, 1)
+        XCTAssertEqual(
+            observer1.startedTestSuites.count, 3,
+            "Three test suites should have started: 'All tests', 'tmp.xctest', and 'Observation'.")
+        XCTAssertEqual(
+            observer2.startedTestSuites.count, 3,
+            "Three test suites should have started: 'All tests', 'tmp.xctest', and 'Observation'.")
+        XCTAssertEqual(observer1.startedTestCaseNames, ["Observation.test_one", "Observation.test_two"])
+        XCTAssertEqual(observer2.startedTestCaseNames, ["Observation.test_one", "Observation.test_two"])
+        XCTAssertEqual(observer1.finishedTestCaseNames,["Observation.test_one"])
+        XCTAssertEqual(observer2.finishedTestCaseNames,["Observation.test_one"])
+        XCTAssertEqual(observer1.finishedBundlePaths.count, 0)
+        XCTAssertEqual(observer2.finishedBundlePaths.count, 0)
+
+        XCTestObservationCenter.shared.removeTestObserver(observer1)
+        XCTestObservationCenter.shared.removeTestObserver(observer2)
+    }
+
+    func test_three() {
+        XCTAssertEqual(observer1.startedBundlePaths.count, 1)
+        XCTAssertEqual(observer2.startedBundlePaths.count, 1)
+        XCTAssertEqual(observer1.startedTestCaseNames, ["Observation.test_one", "Observation.test_two"])
+        XCTAssertEqual(observer2.startedTestCaseNames, ["Observation.test_one", "Observation.test_two"])
+        XCTAssertEqual(observer1.finishedTestCaseNames,["Observation.test_one"])
+        XCTAssertEqual(observer2.finishedTestCaseNames,["Observation.test_one"])
+        XCTAssertEqual(observer1.finishedBundlePaths.count, 0)
+        XCTAssertEqual(observer2.finishedBundlePaths.count, 0)
+
+        XCTestObservationCenter.shared.addTestObserver(observer1)
+        XCTestObservationCenter.shared.addTestObserver(observer2)
+    }
+}
+
+// There's no guarantee as to the order in which these two observers will be
+// called, so we match any order here.
+
+// CHECK: In testSuiteDidFinish\(_:\): Observation
+// CHECK: In testSuiteDidFinish\(_:\): Observation
+
+XCTMain(
+    [testCase(Observation.allTests)],
+    arguments: CommandLine.arguments,
+    observers: [observer1, observer2]
+)
+
+// CHECK: In testSuiteDidFinish\(_:\): .*\.xctest
+// CHECK: In testSuiteDidFinish\(_:\): .*\.xctest
+
+// CHECK: In testSuiteDidFinish\(_:\): All tests
+// CHECK: In testSuiteDidFinish\(_:\): All tests
+
+// CHECK: In testBundleDidFinish\(_:\)
+// CHECK: In testBundleDidFinish\(_:\)