How can I run my performance tests more than ten times?

Question

By default Xcodes performance tests are run ten times and my result is the average of those ten tests. The problem is the averaged result varies considerably each time I run it

Answer 1

a class dump of XCTestCase exposes this method:

- (void)_recordValues:(id)arg1 forPerformanceMetricID:(id)arg2 name:(id)arg3 unitsOfMeasurement:(id)arg4 baselineName:(id)arg5 baselineAverage:(id)arg6 maxPercentRegression:(id)arg7 maxPercentRelativeStandardDeviation:(id)arg8 maxRegression:(id)arg9 maxStandardDeviation:(id)arg10 file:(id)arg11 line:(unsigned long long)arg12;

when this method is swizzled the first parameter (arg1) has the 10 durations:

["0.003544568",
"0.003456569",
"0.003198263",
"0.003257955",
"0.003508724",
"0.003454298",
"0.003461192",
"0.00423787",
"0.003359195",
"0.003335757"]

i added 4 new values (1.0, 2.0, 3.0, 4.0) to the end of this list before passing it back to the original implementation, but unfortunately a different class that observes, XCTestLog, has an internal sanity check that gets tripped:

Assertion failure in +[XCTestLog _messageForTest:didMeasureValues:forPerformanceMetricID:name:unitsOfMeasurement:baselineName:baselineAverage:maxPercentRegression:maxPercentRelativeStandardDeviation:maxRegression:maxStandardDeviation:file:line:]
caught "NSInternalInconsistencyException", "Performance Metrics must provide 10 measurements." 

once the XCTestLog method is also overridden so it doesn't assert, the additional 4 values can be added without any complaints. unfortunately the view still only shows the 10 results.

it does however update the total time + standard deviation values in the mini view.

Before Swizzling

After Swizzling and adding 4 values

in order to view more than 10 results one would probably have to tweak the XCode runtime to tell the table to show more items.