Go test Command

Internal

• go Tool
• Go Testing

Overview

The test command runs tests. The shared flags described here apply:

Shared Flags

For more general details on testing in Go, see:

Go Testing

How go test Works

go test recompiles each package specified in its command line, depending on the mode it is running in (local directory mode or package list mode), along with any files with names matching the file pattern *_test.go and creates a binary test file. The process consists in:

• Creating a work directory (ex: /var/folders/pf/t_bwclcn4mv3kq49ks14_12c0000gn/T/go-build60224940 and subdirectories).
• Creating a vet.cfg file and running go vet on it.
• Creating an importcfg.link file and running the linker on it. The output is the binary test file ([...] -o $WORK/b001/pkg1.test [...]).
• Executing the binary test file as described in Test Execution.

More details about the files that are included and compiles are available in the File Selection section below.

The resulted binary test file that is then executed. More details available in the The Test Binary section.

Local Directory Mode

go test runs in local directory mode when it is invoked with no package argument. In this mode, go test compiles the package sources and tests found in the current directory into a single test binary, and then runs the resulting test binary. Caching is disabled. This seems to assume there's a single package in the directory. What about nested packages? After the package test finishes (what if there are multiple packages?), the runtime prints a summary line with the test status ('ok', 'FAIL', package name and elapsed time).

Package List Mode

go test runs in package list mode when go test is invoked with explicit package arguments (ex: go test math), with the ./... argument or even with .. In this mode the tool independently compiles and tests each of the packages listed on the command line or those implied by ./.... Nested packages are handled as independent packages. If all tests from a package pass, the tool prints only the final 'ok' summary line. If at least one test fails, the tool prints a full test output. Successful package test results are cached to avoid unnecessary repeated running of the test.

File Selection

Upon execution, go test identifies all files that match the *_test.go pattern and compiles them along the package files. These files may contain test functions, benchmark functions, fuzz tests and example functions.

Files whose name begins with "_" (including "_test.go") or "." are ignored.

Test files that declare a package with the suffix "_test" will be compiled as a separate package, and then linked and run with the main test binary.

go test will ignore a directory named "testdata", making it available to hold ancillary data needed by the tests.

More details on writing *_test.go files are available in:

Go Testing | Write a Unit Test

The Test Binary

For each package, go test compiles the package and it links it together with its dependencies into a test binary file named <package-name>.test (example: $WORK/b391/scheduler.test).

As part of building a test binary, go test runs go vet on the package and its test source files to identify significant problems. If go vet finds any problems, go test reports those and does not run the test binary. Only a high-confidence subset of the default go vet checks are used. That subset is: atomic, bool, buildtags, directive, errorsas, ifaceassert, nilfunc, printf, and stringintconv.

Test Execution

The test binary file is executed as such (run go test with -v -x to get this output):

$WORK/b001/pkg1.test -test.paniconexit0 -test.timeout=10m0s -test.v=true -test.count=1

All test output and summary lines are printed to the go command's standard output, even if the test printed them to its own standard error. The go command's standard error is reserved for printing errors building the tests.

Individual Test Function Execution Order

The individual test functions are executed in the order they're declared in the *_test.go file.

If the test functions are specified in more than one *_test.go files, the files are sorted in alphabetical order and their tests are executed in that order. Inside a file, the individual test functions are executed in the order they're declared in the file.

Do Additional Tasks before a Test Function is Run

• Put the initialization tasks in a init() function in the _test.go file. This will run once before the execution of the test functions begins:

package pkg1
[...]
func init() {
}

• Put the task in TestMain() function https://pkg.go.dev/testing#pkg-overview that will be called first and in which you may do additional setup before you call M.Run() http://golang.org/pkg/testing/#M.Run to trigger the execution of test function.

Caching

The rule for a cache hit is that TODO.

Cacheable test flags: -benchtime, -cpu, -list, -parallel, -run, -short, -timeout, -failfast and -v.

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.

go tool reports whether a test result was cached by appending (cached) to the output:

ok  	example.com/experimental-go-module/internal/pkg1	(cached)

Test Coverage

https://medium.com/illumination/a-full-guide-on-coverage-in-golang-95164cdddcd9

go test ./... -count 1 -cover -coverprofile=./build/coverage.out
go tool cover -html=./build/coverage.out -o ./build/coverage.html

Options

-cover

See Test Coverage above.

-ldflags

See:

go build -ldflags