Go test '-run -' flag executes tests much faster

php editor Apple pointed out when introducing the testing framework Go test that using the "-run -" flag can greatly improve the speed of test execution. This flag tells Go test to only run the test function and not any example code. This allows the testing framework to skip unnecessary initialization and cleanup processes, resulting in faster test execution. For developers who need to perform tests frequently, this technique is very useful and can improve work efficiency.

Question content

I am looking at some benchmarks at https://github.com/roaringbitmap/roaring

Use -run - when running a specific benchmark (as mentioned in the comments): go test -bench benchmarknexts -benchmem -run - seems to execute faster, at least running it without -run - seems to have some initial overhead of 5 seconds, which also is drawn:

==roaring==
{1,2,3,4,5,100,1000}
{3,4,1000}
{}
Cardinality:  7
Contains 3?  true
1
3
4
5
1000

Wrote  22  bytes
I wrote the content to a byte stream and read it back.
size before run optimize: 1810 bytes, and after: 38 bytes.

Since the -run flag runs tests based on a regex pattern, it seems like something is being excluded here, but what exactly is it that both run the same tests, the only difference is the initial overhead.

Solution

go test "-run -" flag executes the test much faster

This is the expected result. It's faster when you don't run any tests.

To see what is being executed, add the -v option to the go test execution.

Do not run tests:

go clean -testcache && go test -bench benchmarknexts -benchmem -run - -v

Run all tests:

go clean -testcache && go test -bench benchmarknexts -benchmem -v`

Or, since -run . is equivalent to all tests,

go clean -testcache && go test -bench benchmarknexts -benchmem -run . -v

go is a tool for managing go source code.

Test flag

-run regexp
    Run only those tests, examples, and fuzz tests matching the regular
    expression.

-v
    Verbose output: log all tests as they are run.

Build and test the cache

The go command also caches successful package test results. See "Help Testing" for more information. Running "go clean -testcache" will delete all cached test results (but not cached build results).

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