Make XCTestObservationCenter.shared a class property instead of class function

This change was made in Xcode 9 as part of XCTest's Swiftification effort.

Author: briancroom

Sources/XCTest/Public/XCTestCase+Performance.swift

@@ -157,7 +157,7 @@ extension XCTestCase: PerformanceMeterDelegate {
     }
 
     internal func recordMeasurements(results: String, file: StaticString, line: Int) {
-        XCTestObservationCenter.shared().testCase(self, didMeasurePerformanceResults: results, file: file, line: line)
+        XCTestObservationCenter.shared.testCase(self, didMeasurePerformanceResults: results, file: file, line: line)
     }
 
     internal func recordFailure(description: String, file: StaticString, line: Int) {

Sources/XCTest/Public/XCTestCaseRun.swift

@@ -15,12 +15,12 @@
 open class XCTestCaseRun: XCTestRun {
     open override func start() {
         super.start()
-        XCTestObservationCenter.shared().testCaseWillStart(testCase)
+        XCTestObservationCenter.shared.testCaseWillStart(testCase)
     }
 
     open override func stop() {
         super.stop()
-        XCTestObservationCenter.shared().testCaseDidFinish(testCase)
+        XCTestObservationCenter.shared.testCaseDidFinish(testCase)
     }
 
     open override func recordFailure(withDescription description: String, inFile filePath: String?, atLine lineNumber: Int, expected: Bool) {
@@ -29,7 +29,7 @@ open class XCTestCaseRun: XCTestRun {
             inFile: filePath,
             atLine: lineNumber,
             expected: expected)
-        XCTestObservationCenter.shared().testCase(
+        XCTestObservationCenter.shared.testCase(
             testCase,
             didFailWithDescription: description,
             inFile: filePath,

Sources/XCTest/Public/XCTestMain.swift

@@ -89,7 +89,7 @@ public func XCTMain(_ testCases: [XCTestCaseEntry]) -> Never {
         exit(0)
     case .run(selectedTestName: _):
         // Add a test observer that prints test progress to stdout.
-        let observationCenter = XCTestObservationCenter.shared()
+        let observationCenter = XCTestObservationCenter.shared
         observationCenter.addTestObserver(PrintObserver())
 
         observationCenter.testBundleWillStart(testBundle)

Sources/XCTest/Public/XCTestObservationCenter.swift

@@ -11,18 +11,19 @@
 //  Notification center for test run progress events.
 //
 
+private let _sharedCenter: XCTestObservationCenter = XCTestObservationCenter()
+
 /// Provides a registry for objects wishing to be informed about progress
 /// during the course of a test run. Observers must implement the
 /// `XCTestObservation` protocol
 /// - seealso: `XCTestObservation`
 public class XCTestObservationCenter {
 
-    private static var center = XCTestObservationCenter()
     private var observers = Set<ObjectWrapper<XCTestObservation>>()
 
     /// Registration should be performed on this shared instance
-    public class func shared() -> XCTestObservationCenter {
-        return center
+    public class var shared: XCTestObservationCenter {
+        return _sharedCenter
     }
 
     /// Register an observer to receive future events during a test run. The order

Sources/XCTest/Public/XCTestSuiteRun.swift

@@ -36,12 +36,12 @@ open class XCTestSuiteRun: XCTestRun {
 
     open override func start() {
         super.start()
-        XCTestObservationCenter.shared().testSuiteWillStart(testSuite)
+        XCTestObservationCenter.shared.testSuiteWillStart(testSuite)
     }
 
     open override func stop() {
         super.stop()
-        XCTestObservationCenter.shared().testSuiteDidFinish(testSuite)
+        XCTestObservationCenter.shared.testSuiteDidFinish(testSuite)
     }
 
     /// The test run for each of the tests in this suite.

Tests/Functional/Observation/All/main.swift

@@ -50,7 +50,7 @@ class Observer: XCTestObservation {
 }
 
 let observer = Observer()
-XCTestObservationCenter.shared().addTestObserver(observer)
+XCTestObservationCenter.shared.addTestObserver(observer)
 
 // CHECK: Test Suite 'Observation' started at \d+-\d+-\d+ \d+:\d+:\d+\.\d+
 class Observation: XCTestCase {
@@ -90,7 +90,7 @@ class Observation: XCTestCase {
         XCTAssertEqual(observer.finishedTestCaseNames,["Observation.test_one"])
         XCTAssertEqual(observer.finishedBundlePaths.count, 0)
 
-        XCTestObservationCenter.shared().removeTestObserver(observer)
+        XCTestObservationCenter.shared.removeTestObserver(observer)
     }
 
 // CHECK: Test Case 'Observation.test_three' started at \d+-\d+-\d+ \d+:\d+:\d+\.\d+
@@ -101,7 +101,7 @@ class Observation: XCTestCase {
         XCTAssertEqual(observer.finishedTestCaseNames,["Observation.test_one"])
         XCTAssertEqual(observer.finishedBundlePaths.count, 0)
 
-        XCTestObservationCenter.shared().addTestObserver(observer)
+        XCTestObservationCenter.shared.addTestObserver(observer)
     }
 }
 

Tests/Functional/Observation/Selected/main.swift

@@ -32,7 +32,7 @@ class Observer: XCTestObservation {
 }
 
 let observer = Observer()
-XCTestObservationCenter.shared().addTestObserver(observer)
+XCTestObservationCenter.shared.addTestObserver(observer)
 
 class SkippedTestCase: XCTestCase {
     static var allTests = {