go-internal
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rogpeppe
Allow custom commands to write to stdout and stderr
Hey there, I've had a couple cases where it'd be nice to be able to write to stdout and stderr from inside a custom command.
For example:
func Test(t *testing.T) {
p := testscript.Params{
Cmds: map[string]func(ts *testscript.TestScript, neg bool, args []string){
"render": render,
},
}
testscript.Run(t, p)
}
func render(ts *testscript.TestScript, neg bool, args []string) {
html, err := render.Render(ts.MkAbs(args))
ts.Check(err)
_ = html
}
render 'index.gohtml'
-- index.gohtml --
<html>
<body>
<h1>{{.}}</h1>
</body>
</html>
Unfortunately I haven't found a way to use the command's results within the test. The workaround I use now is to write a file and then read from it.
What I'd like to be able to do is write a testscript like this:
render 'index.gohtml'
stdout '<h1>'
-- index.gohtml --
<html>
<body>
<h1>{{.}}</h1>
</body>
</html>
And the failure case:
! render 'index.gohtml'
stderr 'bad HTML'
-- index.gohtml --
<html
Thanks for extracting and improving this package!
FWIW opened a PR for this one here: https://github.com/rogpeppe/go-internal/pull/140
Picking up API conversation from https://github.com/rogpeppe/go-internal/pull/217#pullrequestreview-1401240139
- Please add a test case for a command that writes to stdout and stderr, and then returns an error. I wonder if stderr is then kept at all, for example.
I don't think this is actually something we can test. A Params.Cmds command has complete control on whether execution is a failure or not. The neg parameter indicates whether the user intended the command to fail or not. So the only "error" situation is when the execution of such a command does not concur with neg. In that situation, execution terminates immediately.
The real problem is the API here. We're trying to work around the fact that a Params.Cmds command should return stdout and stderr, rather than setting it via the approach proposed in #217, an approach which implies it can be done multiple times... which isn't the case. Just as such a command can only call (*TestScript).Fatalf() once.
Fixing this properly, however, would either require us to declare a new API via another field on Params, or by loosening the type of Params.Cmds to allow for functions that have the signature:
func(ts *TestScript, neg bool, args []string) (stdout, stderr string, err error)
