Make it easier to start "cross-test" helper apps in Darwin tests.

We shouldn't require a testcase instance to start such an app, since it's
associated with the test suite, not a specific test.

src/darwin/Framework/CHIPTests/MTRCommissionableBrowserTests.m

@@ -31,8 +31,6 @@
 static const uint16_t kDiscoverDeviceTimeoutInSeconds = 10;
 static const uint16_t kExpectedDiscoveredDevicesCount = 3;
 
-static bool sHelperAppsStarted = false;
-
 // Singleton controller we use.
 static MTRDeviceController * sController = nil;
 
@@ -180,6 +178,18 @@ + (void)setUp
     XCTAssertNotNil(controller);
 
     sController = controller;
+
+    // Start the helper apps our tests use.
+    for (NSString * payload in @[
+             @"MT:Y.K90SO527JA0648G00",
+             @"MT:-24J0AFN00I40648G00",
+         ]) {
+        __auto_type * appRunner = [[MTRTestServerAppRunner alloc] initCrossTestWithAppName:@"all-clusters"
+                                                                                 arguments:@[]
+                                                                                   payload:payload
+                                                                                 testsuite:self];
+        XCTAssertNotNil(appRunner);
+    }
 }
 
 + (void)tearDown
@@ -197,21 +207,6 @@ + (void)tearDown
 - (void)setUp
 {
     [super setUp];
-
-    if (!sHelperAppsStarted) {
-        for (NSString * payload in @[
-                 @"MT:Y.K90SO527JA0648G00",
-                 @"MT:-24J0AFN00I40648G00",
-             ]) {
-            __auto_type * appRunner = [[MTRTestServerAppRunner alloc] initCrossTestWithAppName:@"all-clusters"
-                                                                                     arguments:@[]
-                                                                                       payload:payload
-                                                                                      testcase:self];
-            XCTAssertNotNil(appRunner);
-        }
-        sHelperAppsStarted = true;
-    }
-
     [self setContinueAfterFailure:NO];
 }
 

src/darwin/Framework/CHIPTests/TestHelpers/MTRTestCase.h

@@ -37,6 +37,11 @@ NS_ASSUME_NONNULL_BEGIN
  */
 - (NSTask *)createTaskForPath:(NSString *)path;
 
+/**
+ * Same thing, but not tied to a specific testcase instance.
+ */
++ (NSTask *)createTaskForPath:(NSString *)path;
+
 /**
  * Run a task to completion and make sure it succeeds.
  */
@@ -52,14 +57,19 @@ NS_ASSUME_NONNULL_BEGIN
  * Launch a cross-test task.  The task will be automatically terminated when the testsuite
  * tearDown happens.
  */
-- (void)launchCrossTestTask:(NSTask *)task;
++ (void)launchCrossTestTask:(NSTask *)task;
 #endif // HAVE_NSTASK
 
 /**
  * Get an absolute path from a path relative to the Matter SDK root.
  */
 - (NSString *)absolutePathFor:(NSString *)matterRootRelativePath;
 
+/**
+ * Same thing, but not tied to a specific testcase instance.
+ */
++ (NSString *)absolutePathFor:(NSString *)matterRootRelativePath;
+
 @end
 
 NS_ASSUME_NONNULL_END

src/darwin/Framework/CHIPTests/TestHelpers/MTRTestCase.mm

@@ -85,13 +85,18 @@ - (void)tearDown
 }
 
 #if HAVE_NSTASK
-- (NSTask *)createTaskForPath:(NSString *)path
++ (NSTask *)createTaskForPath:(NSString *)path
 {
     NSTask * task = [[NSTask alloc] init];
     [task setLaunchPath:[self absolutePathFor:path]];
     return task;
 }
 
+- (NSTask *)createTaskForPath:(NSString *)path
+{
+    return [self.class createTaskForPath:path];
+}
+
 - (void)runTask:(NSTask *)task
 {
     NSError * launchError;
@@ -102,7 +107,7 @@ - (void)runTask:(NSTask *)task
     XCTAssertEqual([task terminationStatus], 0);
 }
 
-- (void)doLaunchTask:(NSTask *)task
++ (void)doLaunchTask:(NSTask *)task
 {
     NSError * launchError;
     [task launchAndReturnError:&launchError];
@@ -111,20 +116,20 @@ - (void)doLaunchTask:(NSTask *)task
 
 - (void)launchTask:(NSTask *)task
 {
-    [self doLaunchTask:task];
+    [self.class doLaunchTask:task];
 
     [_runningTasks addObject:task];
 }
 
-- (void)launchCrossTestTask:(NSTask *)task
++ (void)launchCrossTestTask:(NSTask *)task
 {
     [self doLaunchTask:task];
 
     [runningCrossTestTasks addObject:task];
 }
 #endif // HAVE_NSTASK
 
-- (NSString *)absolutePathFor:(NSString *)matterRootRelativePath
++ (NSString *)absolutePathFor:(NSString *)matterRootRelativePath
 {
     // Start with the absolute path to our file, then remove the suffix that
     // comes after the path to the Matter SDK root.
@@ -135,4 +140,8 @@ - (NSString *)absolutePathFor:(NSString *)matterRootRelativePath
     return [NSString pathWithComponents:pathComponents];
 }
 
+- (NSString *)absolutePathFor:(NSString *)matterRootRelativePath
+{
+    return [self.class absolutePathFor:matterRootRelativePath];
+}
 @end

src/darwin/Framework/CHIPTests/TestHelpers/MTRTestServerAppRunner.h

@@ -48,8 +48,10 @@ NS_ASSUME_NONNULL_BEGIN
 /**
  * Same thing, but initialize as a "cross test" helper, which is not killed at
  * the end of the current test (but is killed at the end of the current suite).
+ *
+ * The passed-in testsuite must be a subclass of MTRTestCase.
  */
-- (instancetype)initCrossTestWithAppName:(NSString *)name arguments:(NSArray<NSString *> *)arguments payload:(NSString *)payload testcase:(MTRTestCase *)testcase;
+- (instancetype)initCrossTestWithAppName:(NSString *)name arguments:(NSArray<NSString *> *)arguments payload:(NSString *)payload testsuite:(Class)testsuite;
 
 /**
  * Get the unique index that will be used for the next initialization.  This

src/darwin/Framework/CHIPTests/TestHelpers/MTRTestServerAppRunner.m

@@ -36,7 +36,7 @@ @implementation MTRTestServerAppRunner {
 #endif
 }
 
-- (instancetype)initInternalWithAppName:(NSString *)name arguments:(NSArray<NSString *> *)arguments payload:(NSString *)payload testcase:(MTRTestCase *)testcase isCrossTest:(BOOL)isCrossTest
+- (instancetype)initInternalWithAppName:(NSString *)name arguments:(NSArray<NSString *> *)arguments payload:(NSString *)payload
 {
 #if !HAVE_NSTASK
     XCTFail("Unable to start server app when we do not have NSTask");
@@ -61,7 +61,7 @@ - (instancetype)initInternalWithAppName:(NSString *)name arguments:(NSArray<NSSt
     NSNumber * passcode = parsedPayload.setupPasscode;
 
     __auto_type * executable = [NSString stringWithFormat:@"out/debug/%@-app/chip-%@-app", name, name];
-    _appTask = [testcase createTaskForPath:executable];
+    _appTask = [MTRTestCase createTaskForPath:executable];
 
     __auto_type * forcedArguments = @[
         // Make sure we only advertise on the local interface.
@@ -92,12 +92,6 @@ - (instancetype)initInternalWithAppName:(NSString *)name arguments:(NSArray<NSSt
     _appTask.standardOutput = [NSFileHandle fileHandleForWritingAtPath:outFile];
     _appTask.standardError = [NSFileHandle fileHandleForWritingAtPath:errorFile];
 
-    if (isCrossTest) {
-        [testcase launchCrossTestTask:_appTask];
-    } else {
-        [testcase launchTask:_appTask];
-    }
-
     NSLog(@"Started chip-%@-app (%@) with arguments %@ stdout=%@ and stderr=%@", name, _appTask, allArguments, outFile, errorFile);
 
     return self;
@@ -106,12 +100,29 @@ - (instancetype)initInternalWithAppName:(NSString *)name arguments:(NSArray<NSSt
 
 - (instancetype)initWithAppName:(NSString *)name arguments:(NSArray<NSString *> *)arguments payload:(NSString *)payload testcase:(MTRTestCase *)testcase
 {
-    return [self initInternalWithAppName:name arguments:arguments payload:payload testcase:testcase isCrossTest:NO];
+    if (!(self = [self initInternalWithAppName:name arguments:arguments payload:payload])) {
+        return nil;
+    }
+
+    [testcase launchTask:_appTask];
+
+    return self;
 }
 
-- (instancetype)initCrossTestWithAppName:(NSString *)name arguments:(NSArray<NSString *> *)arguments payload:(NSString *)payload testcase:(MTRTestCase *)testcase
+- (instancetype)initCrossTestWithAppName:(NSString *)name arguments:(NSArray<NSString *> *)arguments payload:(NSString *)payload testsuite:(Class)testsuite
 {
-    return [self initInternalWithAppName:name arguments:arguments payload:payload testcase:testcase isCrossTest:YES];
+    if (![testsuite isSubclassOfClass:MTRTestCase.class]) {
+        NSLog(@"%@ is not a subclass of MTRTestCase", testsuite);
+        return nil;
+    }
+
+    if (!(self = [self initInternalWithAppName:name arguments:arguments payload:payload])) {
+        return nil;
+    }
+
+    [MTRTestCase launchCrossTestTask:_appTask];
+
+    return self;
 }
 
 + (unsigned)nextUniqueIndex