Go 1.9 adds a new feature described at https://beta.golang.org/doc/go1.9#go-test-list:

The go test command accepts a new -list flag, which takes a regular expression as an argument and prints to stdout the name of any tests, benchmarks, or examples that match it, without running them.

go test -help says:

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

It's issue #17209, implemented in CL 41195 (ba8ff87). /cc @nemith @mpvl

What version of Go are you using (go version)?

go version go1.9rc1 darwin/amd64

What operating system and processor architecture are you using (go env)?

$ go env
GOARCH="amd64"
GOBIN=""
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOOS="darwin"
GOPATH="/Users/Dmitri/Dropbox/Work/2013/GoLanding:/Users/Dmitri/Dropbox/Work/2013/GoLand"
GORACE=""
GOROOT="/usr/local/go"
GOTOOLDIR="/usr/local/go/pkg/tool/darwin_amd64"
GCCGO="gccgo"
CC="clang"
GOGCCFLAGS="-fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/tw/kgz4v2kn4n7d7ryg5k_z3dk40000gn/T/go-build927351599=/tmp/go-build -gno-record-gcc-switches -fno-common"
CXX="clang++"
CGO_ENABLED="1"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"

What did you do?

I ran go test -v and go test -list=Example on a sample package with 3 examples, two of which are runnable (i.e., they have a "Output:" comment at the end), and one is not runnable (no "Output:" comment):

package main_test

import "fmt"

func ExampleLoud() {
	// Dog says:
	fmt.Println("BARK!")

	// Output: BARK!
}

func ExampleQuiet() {
	// Gopher says:
	fmt.Println("")

	// Output:
}

func ExampleNoOutput() {
	// This example has no "Output:" comment at the end,
	// so it doesn't get run, it's just shown in docs and
	// ensured to build without errors.

	_ = fmt.Sprintln("*tree falling sound*")
}

Note, the above is just a minimal reproduce sample. I ran into this issue in a real Go package github.com/shurcooL/issuesapp/httpclient:

httpclient $ go test -v
=== RUN   ExampleNewIssues
--- PASS: ExampleNewIssues (0.00s)
=== RUN   ExampleNewIssues_authenticated
--- PASS: ExampleNewIssues_authenticated (0.00s)
=== RUN   ExampleIssues_List
--- PASS: ExampleIssues_List (0.00s)
=== RUN   ExampleIssues_Count
--- PASS: ExampleIssues_Count (0.00s)
=== RUN   ExampleIssues_ListComments
--- PASS: ExampleIssues_ListComments (0.00s)
PASS
ok  	github.com/shurcooL/issuesapp/httpclient	0.011s
httpclient $ go test -list=Example
ExampleIssues_List
ExampleIssues_Count
ExampleIssues_ListComments
ok  	github.com/shurcooL/issuesapp/httpclient	0.012s
httpclient $ 

What did you expect to see?

$ go test -v
=== RUN   ExampleLoud
--- PASS: ExampleLoud (0.00s)
=== RUN   ExampleQuiet
--- PASS: ExampleQuiet (0.00s)
PASS
ok  	sample/package	0.006s
$ go test -list=Example
ExampleLoud
ExampleQuiet
ok  	sample/package	0.005s
$ 

What did you see instead?

$ go test -v
=== RUN   ExampleLoud
--- PASS: ExampleLoud (0.00s)
=== RUN   ExampleQuiet
--- PASS: ExampleQuiet (0.00s)
PASS
ok  	sample/package	0.006s
$ go test -list=Example
ExampleLoud
ok  	sample/package	0.005s
$ 

ExampleQuiet is not listed in go test -list=Example output, even though it's a valid runnable example [1] that runs as part of go test -v.

[1] https://golang.org/cmd/go/#hdr-Description_of_testing_functions

Cause

The cause is simple and can be seen in the code implementing the feature at ba8ff87#diff-70e628298261565d825f7199d13042f2R972. testing.listTests function has this loop for printing examples:

for _, example := range examples {
	if ok, _ := matchString(*matchList, example.Name); ok && example.Output != "" {
		fmt.Println(example.Name)
	}
}

Notably, it checks that example.Output != "". I'm assuming it does that to try to find runnable examples. However, some runnable examples (i.e., ones with last comment that starts with "Output:" or "Unordered output:") have empty expected output.

They're still runnable, and should be included in output of go test -list, just like they are in output of go test -v.