How to find the slowest XCTest

We can distinguish between performance of different kinds of tests in the context of iOS development: unit tests are expected to run very fast because they should not touch any I/O do network calls or fire timers, integration tests are slower since they involve I/O or network or interaction between multiple components including external parties, acceptance tests are the slowest since a whole system is under test. Functional or UI snapshot tests are somewhere in between.

Whatever the tests you're working on, there might be room for improvements. The following is simple but useful command based on awk that can help you to identify the slowest tests in your XCTest-based test suite.

First, you need to get the output log produced by your XCTest-based test target and store it to a file. You can either copy and paste the build log from Xcode, after you have run Command + U, or use the following command that runs xcodebuild test:

xcodebuild -project YourProject.xcodeproj \
           -scheme YourProject \
           -destination 'platform=iOS Simulator,name=iPhone 6s Plus,OS=9.3' \
           test \
           | tee ./xcodebuild.log

When you have xcodebuild.log in place, run:

cat xcodebuild.log | grep 'TestCase.*seconds' | awk -F '[()]' '{print $2 " -> " $1}' | sort -rn | head -5

The output you'll receive will look like this (these are the 5 slowest tests in a suite):

1.957 seconds -> Test Case 'A...' passed
0.279 seconds -> Test Case 'B...' passed
0.274 seconds -> Test Case 'C...' passed
0.248 seconds -> Test Case 'D...' passed
0.201 seconds -> Test Case 'E...' passed

The trick is to use awk to capture time using regular expression [()] (left or right brace) that matches round braces in an original string produced by xcodebuild like:

Test Case 'E...' passed (0.201 seconds).

awk puts numbers to be the first symbols in a resulting string, skips the braces, and that makes resulting string available for numeric sort, the rest is self-explanatory.

I found this command particularly useful when I was looking at how to optimize the running time of a unit test suite I was working on. I found that some of the tests were taking 300 milliseconds to run which was unacceptable for a unit test suite of several hundreds of tests.

Hopefully, someone will also benefit from this simple solution. Let your tests be fast!

Note: Perl can also be used instead of awk:

perl -ne '/(TestCase.*)\((.*)\)/ && print $2 . " -> " . $1 . "\n"' xcodebuild.log`.