Repository: go
Issue: x/tools/gopls: fails to detect tests starting with an underscore
Labels: gopls,Tools,gopls/analysis

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### What version of Go, VS Code & VS Code Go extension are you using?
<details><summary>Version Information</summary><br>

* Run `go version` to get version of Go from _the VS Code integrated terminal_.
	- go1.23.4 linux/amd64
* Run `gopls -v version` to get version of Gopls from _the VS Code integrated terminal_.
	- golang.org/x/tools/gopls v0.17.0-pre.4
* Run `code -v` or `code-insiders -v` to get version of VS Code or VS Code Insiders.
	- 1.96.0 138f619c86f1199955d53b4166bef66ef252935c x64
* Check your installed extensions to get the version of the VS Code Go extension
	- 0.43.4 (pre-release)
* Run Ctrl+Shift+P (Cmd+Shift+P on Mac OS) > `Go: Locate Configured Go Tools` command.
	- <Paste the output here>
</details>

### Share the Go related settings you have added/edited

Run `Preferences: Open Settings (JSON)` command to open your settings.json file.
Share all the settings with the `go.` or `["go"]` or `gopls` prefixes.

### Describe the bug

The new experimental Go Companion tests infrastructure ignores tests whose name (other than the `Test`) prefix starts with an underscore, while `go test` does not.

### Steps to reproduce the behavior:
1. Create a new empty package with a test file in it
2. Create a test named `Test_foo`
3. Run `go test -v ./...` within that package -- observe the test is run
4. Enable the Go Companion experimental test explorer and code lens
5. Observe that the companion doesn't detect the test, and so the code lens is hidden, and the package (lacking any other tests) is omitted from the test explorer
6. Change the test name to `TestX_foo`
7. Observe that Go Companion sees the test now
8. Extra fun: rename it back. Observe that at least sometimes Go Companion still sees the test with the _old_ name as existing, and shows the code lens and the entry in the test explorer, but since it tries to run it with the old name, it doesn't work / produces no results.

The `Test_foo` naming pattern in my case came from "generate tests for function" helper for a non-exported method on a non-exported type, so the test name I have is `Test_typeName_methodName`

Spun out of a prior discussion with @firelizzard18: https://github.com/golang/vscode-go/issues/1636#issuecomment-2540066996

This feels like it might be a bug in gopls, if the extension is just asking it to list discovered tests, but I'm not sure how to confirm that.

### Screenshots or recordings

N/A