GO-TESTFLAG(7)

NAME
go - tool for managing Go source code

DESCRIPTION
The ‘go test’ command takes both flags that apply to ‘go test’ itself and flags that apply to the resulting test binary.

Several of the flags control profiling and write an execution profile suitable for "go tool pprof"; run "go tool pprof -h" for more information. The --alloc_space, --alloc_objects, and --show_bytes options of pprof control how the information is presented.

The following flags are recognized by the ‘go test’ command and control the execution of any test:

-bench regexp
    Run only those benchmarks matching a regular expression. By default, no benchmarks are run. To run all benchmarks, use ‘-bench .’ or ‘-bench=.’. The regular expression is split by unbracketed slash (/) characters into a sequence of regular expressions, and each part of a benchmark’s identifier must match the corresponding element in the sequence, if any. Possible parents of matches are run with b.N=1 to identify sub-benchmarks. For example, given -bench=X/Y, top-level benchmarks matching X are run with b.N=1 to find any sub-benchmarks matching Y, which are then run in full.

-benchtime t
    Run enough iterations of each benchmark to take t, specified as a time.Duration (for example, -benchtime 1h30s).
    The default is 1 second (1s).
    The special syntax Nx means to run the benchmark N times (for example, -benchtime 100x).

-count n
    Run each test, benchmark, and fuzz seed n times (default 1).
    If -cpu is set, run n times for each GOMAXPROCS value.
    Examples are always run once. -count does not apply to fuzz tests matched by -fuzz.

-cover
    Enable coverage analysis.
    Note that because coverage works by annotating the source code before compilation, compilation and test failures with coverage enabled may report line numbers that don’t correspond to the original sources.

-covermode set,count,atomic
    Set the mode for coverage analysis for the package[s] being tested. The default is "set" unless -race is enabled, in which case it is "atomic".
    The values:
        set: bool: does this statement run?
        count: int: how many times does this statement run?
        atomic: int: count, but correct in multithreaded tests;
                significantly more expensive.
    Sets -cover.

-coverpkg pattern1,pattern2,pattern3
    Apply coverage analysis in each test to packages matching the patterns. The default is for each test to analyze only the package being tested.
    See ‘go help packages’ for a description of package patterns.
    Sets -cover.

-cpu 1,2,4
    Specify a list of GOMAXPROCS values for which the tests, benchmarks or fuzz tests should be executed. The default is the current value of GOMAXPROCS. -cpu does not apply to fuzz tests matched by -fuzz.

-failfast
    Do not start new tests after the first test failure.

-fuzz regexp
    Run the fuzz test matching the regular expression. When specified, the command line argument must match exactly one package within the main module, and regexp must match exactly one fuzz test within that package. Fuzzing will occur after tests, benchmarks, seed corpora of other fuzz tests, and examples have completed. See the Fuzzing section of the testing package documentation for details.

-fuzztime t
    Run enough iterations of the fuzz target during fuzzing to take t, specified as a time.Duration (for example, -fuzztime 1h30s).
        The default is to run forever.
    The special syntax Nx means to run the fuzz target N times (for example, -fuzztime 1000x).

-fuzzminimizetime t
    Run enough iterations of the fuzz target during each minimization attempt to take t, as specified as a time.Duration (for example, -fuzzminimizetime 30s).
        The default is 60s.
    The special syntax Nx means to run the fuzz target N times (for example, -fuzzminimizetime 100x).

-json
    Log verbose output and test results in JSON. This presents the same information as the -v flag in a machine-readable format.

-list regexp
    List tests, benchmarks, fuzz tests, or examples matching the regular expression. No tests, benchmarks, fuzz tests, or examples will be run. This will only list top-level tests. No subtest or subbenchmarks will be shown.

-parallel n
    Allow parallel execution of test functions that call t.Parallel, and fuzz targets that call t.Parallel when running the seed corpus. The value of this flag is the maximum number of tests to run simultaneously.
    While fuzzing, the value of this flag is the maximum number of subprocesses that may call the fuzz function simultaneously, regardless of whether T.Parallel is called.
    By default, -parallel is set to the value of GOMAXPROCS. Setting -parallel to values higher than GOMAXPROCS may cause degraded performance due to CPU contention, especially when fuzzing. Note that -parallel only applies within a single test binary. The ‘go test’ command may run tests for different packages in parallel as well, according to the setting of the -p flag (see ‘go help build’).

-run regexp
    Run only those tests, examples, and fuzz tests matching the regular expression. For tests, the regular expression is split by unbracketed slash (/) characters into a sequence of regular expressions, and each part of a test’s identifier must match the corresponding element in the sequence, if any. Note that possible parents of matches are run too, so that -run=X/Y matches and runs and reports the result of all tests matching X, even those without sub-tests matching Y, because it must run them to look for those sub-tests.

-short
    Tell long-running tests to shorten their run time. It is off by default but set during all.bash so that installing the Go tree can run a sanity check but not spend time running exhaustive tests.

-shuffle off,on,N
    Randomize the execution order of tests and benchmarks. It is off by default. If -shuffle is set to on, then it will seed the randomizer using the system clock. If -shuffle is set to an integer N, then N will be used as the seed value. In both cases, the seed will be reported for reproducibility.

-timeout d
    If a test binary runs longer than duration d, panic.
    If d is 0, the timeout is disabled.
    The default is 10 minutes (10m).

-v  Verbose output: log all tests as they are run. Also print all text from Log and Logf calls even if the test succeeds.

-vet list
    Configure the invocation of "go vet" during "go test" to use the comma-separated list of vet checks.
    If list is empty, "go test" runs "go vet" with a curated list of checks believed to be always worth addressing.
    If list is "off", "go test" does not run "go vet" at all.

The following flags are also recognized by ‘go test’ and can be used to profile the tests during execution:

-benchmem
    Print memory allocation statistics for benchmarks.

-blockprofile block.out
    Write a goroutine blocking profile to the specified file when all tests are complete.
    Writes test binary as -c would.

-blockprofilerate n
    Control the detail provided in goroutine blocking profiles by calling runtime.SetBlockProfileRate with n.
    See ‘go doc runtime.SetBlockProfileRate’.
    The profiler aims to sample, on average, one blocking event every n nanoseconds the program spends blocked. By default, if -test.blockprofile is set without this flag, all blocking events are recorded, equivalent to -test.blockprofilerate=1.

-coverprofile cover.out
    Write a coverage profile to the file after all tests have passed.
    Sets -cover.

-cpuprofile cpu.out
    Write a CPU profile to the specified file before exiting.
    Writes test binary as -c would.

-memprofile mem.out
    Write an allocation profile to the file after all tests have passed.
    Writes test binary as -c would.

-memprofilerate n
    Enable more precise (and expensive) memory allocation profiles by setting runtime.MemProfileRate. See ‘go doc runtime.MemProfileRate’. To profile all memory allocations, use -test.memprofilerate=1.

-mutexprofile mutex.out
    Write a mutex contention profile to the specified file when all tests are complete.
    Writes test binary as -c would.

-mutexprofilefraction n
    Sample 1 in n stack traces of goroutines holding a contended mutex.

-outputdir directory
    Place output files from profiling in the specified directory, by default the directory in which "go test" is running.

-trace trace.out
    Write an execution trace to the specified file before exiting.

Each of these flags is also recognized with an optional ‘test.’ prefix, as in -test.v. When invoking the generated test binary (the result of ‘go test -c’) directly, however, the prefix is mandatory.

The ‘go test’ command rewrites or removes recognized flags, as appropriate, both before and after the optional package list, before invoking the test binary.

For instance, the command

    go test -v -myflag testdata -cpuprofile=prof.out -x

will compile the test binary and then run it as

    pkg.test -test.v -myflag testdata -test.cpuprofile=prof.out

(The -x flag is removed because it applies only to the go command’s execution, not to the test itself.)

The test flags that generate profiles (other than for coverage) also leave the test binary in pkg.test for use when analyzing the profiles.

When ‘go test’ runs a test binary, it does so from within the corresponding package’s source code directory. Depending on the test, it may be necessary to do the same when invoking a generated test binary directly. Because that directory may be located within the module cache, which may be read-only and is verified by checksums, the test must not write to it or any other directory within the module unless explicitly requested by the user (such as with the -fuzz flag, which writes failures to testdata/fuzz).

The command-line package list, if present, must appear before any flag not known to the go test command. Continuing the example above, the package list would have to appear before -myflag, but could appear on either side of -v.

When ‘go test’ runs in package list mode, ‘go test’ caches successful package test results to avoid unnecessary repeated running of tests. To disable test caching, use any test flag or argument other than the cacheable flags. The idiomatic way to disable test caching explicitly is to use -count=1.

To keep an argument for a test binary from being interpreted as a known flag or a package name, use -args (see ‘go help test’) which passes the remainder of the command line through to the test binary uninterpreted and unaltered.

For instance, the command

    go test -v -args -x -v

will compile the test binary and then run it as

    pkg.test -test.v -x -v

Similarly,

    go test -args math

will compile the test binary and then run it as

    pkg.test math

In the first example, the -x and the second -v are passed through to the test binary unchanged and with no effect on the go command itself. In the second example, the argument math is passed through to the test binary, instead of being interpreted as the package list.

AUTHOR

This manual page was written by Michael Stapelberg <stapelberg@debian.org> and is maintained by the Debian Go Compiler Team <team+go-compiler@tracker.debian.org> based on the output of ‘go help testflag’ for the Debian project (and may be used by others).