Cannot test FlagTracker using a file data source

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.

launchdarkly / go-server-sdk

Cannot test FlagTracker using a file data source #156