Cannot test FlagTracker using a file data source

[constant-mihai]

Is this a support request?
No.

Describe the bug
I'm trying to write unit tests for some code which uses FlagTracker.
I have successfully used test data sources for testing flag queries but cannot seem to do so for the flag listener, nor for the flag value listener.
After reading the docs for the FlagTracker interface, I've learned that:

	// Change events only work if the SDK is actually connecting to LaunchDarkly (or using the file data source).
	// If the SDK is only reading flags from a database (ldcomponents.ExternalUpdatesOnly) then it cannot
	// know when there is a change, because flags are read on an as-needed basis.

File data sources do not seem to work either.

To reproduce
Run the following program:

package main

import (
	"fmt"
	"os"
	"os/signal"
	"syscall"
	"time"

	"gopkg.in/launchdarkly/go-sdk-common.v2/lduser"
	sdk "gopkg.in/launchdarkly/go-server-sdk.v5"
	"gopkg.in/launchdarkly/go-server-sdk.v5/ldcomponents"
	"gopkg.in/launchdarkly/go-server-sdk.v5/ldfiledata"
	"gopkg.in/launchdarkly/go-server-sdk.v5/ldfilewatch"
)

func main() {
	sigs := make(chan os.Signal, 1)
	signal.Notify(sigs, syscall.SIGINT, syscall.SIGTERM)

	ldClient, _ := sdk.MakeCustomClient("sdk-key-123abc",
		sdk.Config{
			Events: ldcomponents.NoEvents(),
			DataSource: ldfiledata.DataSource().
				FilePaths("./ld-simple.yaml").
				Reloader(ldfilewatch.WatchFiles),
		}, 0)

	// Not sure how MakeCustomClient works, so I'm putting a sleep here.
	time.Sleep(3 * time.Second)
	context := lduser.NewUserBuilder("user-key-1").Build()
	optIn, err := ldClient.BoolVariation("opt-in", context, false)
	if err != nil {
		fmt.Printf("%s\n", err.Error())
		return
	}
	fmt.Printf("opt-in: %v\n", optIn)

	updateCh := ldClient.GetFlagTracker().AddFlagChangeListener()
	defer func() {
		ldClient.GetFlagTracker().RemoveFlagChangeListener(updateCh)
	}()

	for {
		select {
		case <-sigs:
			return
		case event, ok := <-updateCh:
			if !ok {
				// channel closed
				return
			}
			fmt.Printf("event: %v\n", event)
		}
	}
}

ld-simple.yaml

flagValues:
  opt-in: true

Program prints:

[LaunchDarkly] 2024/06/17 10:25:33 INFO: Starting LaunchDarkly client 5.10.1
[LaunchDarkly] 2024/06/17 10:25:33 INFO: FileDataSource: Reloading flag data after detecting a change
opt-in: true

Expected behavior
Expected the program to print:

[LaunchDarkly] 2024/06/17 10:25:33 INFO: Starting LaunchDarkly client 5.10.1
[LaunchDarkly] 2024/06/17 10:25:33 INFO: FileDataSource: Reloading flag data after detecting a change
opt-in: true
event: <some event value>

Logs
See above.

SDK version
5.10.1

Language version, developer tools
go 1.22.1

OS/platform
Ubuntu 22.04

Additional context
N/A.

[cwaldren-ld]

Hi @constant-mihai , I will take a look at this.

As I mentioned on your other issue, the 5.10 version went end-of-life on December 7th of 2023, and is not supported by LaunchDarkly. If this turns out to need a bugfix, the fix would not be backported to v5.

Filed internally as 247611.