refactor: replace lopg.ObserverLogs with logptest (#252)

## What does this PR do?

ObserverLogs is relying on a testing package in a non-test package

move to logptest

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Author: kruskall

go.mod

@@ -4,7 +4,7 @@ go 1.23.0
 
 require (
 	github.com/docker/docker v26.1.5+incompatible
-	github.com/elastic/elastic-agent-libs v0.20.0
+	github.com/elastic/elastic-agent-libs v0.21.6
 	github.com/elastic/go-licenser v0.4.2
 	github.com/elastic/go-structform v0.0.9
 	github.com/elastic/go-sysinfo v1.14.1

go.sum

@@ -21,8 +21,8 @@ github.com/docker/go-connections v0.4.0 h1:El9xVISelRB7BuFusrZozjnkIM5YnzCViNKoh
 github.com/docker/go-connections v0.4.0/go.mod h1:Gbd7IOopHjR8Iph03tsViu4nIes5XhDvyHbTtUxmeec=
 github.com/docker/go-units v0.5.0 h1:69rxXcBk27SvSaaxTtLh/8llcHD8vYHT7WSdRZ/jvr4=
 github.com/docker/go-units v0.5.0/go.mod h1:fgPhTUdO+D/Jk86RDLlptpiXQzgHJF7gydDDbaIK4Dk=
-github.com/elastic/elastic-agent-libs v0.20.0 h1:MPjenwuEr+QfMeQRV4BK817ZbiNS38SXJE7QGHDwhUs=
-github.com/elastic/elastic-agent-libs v0.20.0/go.mod h1:1HNxREH8C27kGrJCtKZh/ot8pV8joH8VREP21+FrH5s=
+github.com/elastic/elastic-agent-libs v0.21.6 h1:hvBAi4KHaYf4hn+rTc9m6A35eZjqb1uoE2exklIdWm0=
+github.com/elastic/elastic-agent-libs v0.21.6/go.mod h1:xSeIP3NtOIT4N2pPS4EyURmS1Q8mK0lWZ8Wd1Du6q3w=
 github.com/elastic/go-licenser v0.4.2 h1:bPbGm8bUd8rxzSswFOqvQh1dAkKGkgAmrPxbUi+Y9+A=
 github.com/elastic/go-licenser v0.4.2/go.mod h1:W8eH6FaZDR8fQGm+7FnVa7MxI1b/6dAqxz+zPB8nm5c=
 github.com/elastic/go-structform v0.0.9 h1:HpcS7xljL4kSyUfDJ8cXTJC6rU5ChL1wYb6cx3HLD+o=

metric/system/process/process_common.go

@@ -157,7 +157,9 @@ var PidStates = map[byte]PidState{
 // Init initializes a Stats instance. It returns errors if the provided process regexes
 // cannot be compiled.
 func (procStats *Stats) Init() error {
-	procStats.logger = logp.NewLogger("processes")
+	if procStats.logger == nil {
+		procStats.logger = logp.NewLogger("processes")
+	}
 	var err error
 	procStats.host, err = sysinfo.Host()
 	if err != nil {

metric/system/process/process_linux_test.go

@@ -30,6 +30,7 @@ import (
 	"github.com/stretchr/testify/require"
 
 	"github.com/elastic/elastic-agent-libs/logp"
+	"github.com/elastic/elastic-agent-libs/logp/logptest"
 	"github.com/elastic/elastic-agent-libs/opt"
 	"github.com/elastic/elastic-agent-system-metrics/dev-tools/systemtests"
 	"github.com/elastic/elastic-agent-system-metrics/metric/system/cgroup"
@@ -182,12 +183,14 @@ func TestParseProcStat(t *testing.T) {
 
 func TestCgroupsBadCgroupsConfig(t *testing.T) {
 	rootfs := systemtests.DockerTestResolver()
-	_ = logp.DevelopmentSetup(logp.ToObserverOutput())
-	testStats := Stats{CPUTicks: true,
+	logger, observedLogs := logptest.NewTestingLoggerWithObserver(t, "")
+	testStats := Stats{
+		CPUTicks:      true,
 		EnableCgroups: true,
 		EnableNetwork: true,
 		Hostfs:        rootfs,
 		Procs:         []string{".*"},
+		logger:        logger,
 		CgroupOpts:    cgroup.ReaderOptions{RootfsMountpoint: resolve.NewTestResolver("testdata")}, // procs here have no cgroup data, leading to errors
 	}
 	err := testStats.Init()
@@ -202,7 +205,7 @@ func TestCgroupsBadCgroupsConfig(t *testing.T) {
 	t.Logf("got %d procs", len(procs))
 	require.NotEmpty(t, procs)
 
-	gotLogs := logp.ObserverLogs().TakeAll()
+	gotLogs := observedLogs.TakeAll()
 	// check to see if we got the "correct" error message
 	foundLogEntry := false