Guard against possible race conditions in RCTAllocationTests

Reviewed By: javache

Differential Revision: D3829341

fbshipit-source-id: 2a3fd66a7b1494176726a79ef28cef5158d8ad58

Examples/UIExplorer/UIExplorerUnitTests/RCTAllocationTests.m

@@ -85,9 +85,14 @@ - (void)setUp
 
   NSURL *tempDir = [NSURL fileURLWithPath:NSTemporaryDirectory() isDirectory:YES];
   [[NSFileManager defaultManager] createDirectoryAtURL:tempDir withIntermediateDirectories:YES attributes:nil error:NULL];
-
-  _bundleURL = [tempDir URLByAppendingPathComponent:@"rctallocationtests-bundle.js"];
-  [bundleContents writeToURL:_bundleURL atomically:YES encoding:NSUTF8StringEncoding error:NULL];
+  NSString *guid = [[NSProcessInfo processInfo] globallyUniqueString];
+  NSString *fileName = [NSString stringWithFormat:@"rctallocationtests-bundle-%@.js", guid];
+
+  _bundleURL = [tempDir URLByAppendingPathComponent:fileName];
+  NSError *saveError;
+  if (![bundleContents writeToURL:_bundleURL atomically:YES encoding:NSUTF8StringEncoding error:&saveError]) {
+    XCTFail(@"Failed to save test bundle to %@, error: %@", _bundleURL, saveError);
+  };
 }
 
 - (void)tearDown