Fix typo in float format for APM_SAMPLING_RATE (#5712)

* Fix float format for APM_SAMPLING_RATE

internal/pkg/agent/cmd/run.go

@@ -627,7 +627,7 @@ func initTracer(agentName, version string, mcfg *monitoringCfg.MonitoringConfig)
 		defer os.Unsetenv(envCACert)
 	}
 	if cfg.SamplingRate != nil {
-		os.Setenv(envSampleRate, strconv.FormatFloat(float64(*cfg.SamplingRate), 'b', -1, 32))
+		os.Setenv(envSampleRate, strconv.FormatFloat(float64(*cfg.SamplingRate), 'f', -1, 32))
 		defer os.Unsetenv(envSampleRate)
 	}
 

internal/pkg/agent/cmd/run_test.go

@@ -0,0 +1,95 @@
+// Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+// or more contributor license agreements. Licensed under the Elastic License 2.0;
+// you may not use this file except in compliance with the Elastic License 2.0.
+
+package cmd
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+
+	monitoringCfg "github.com/elastic/elastic-agent/internal/pkg/core/monitoring/config"
+)
+
+func Test_initTracer(t *testing.T) {
+	tenPercentSamplingRate := float32(0.1)
+
+	type args struct {
+		agentName string
+		version   string
+		mcfg      *monitoringCfg.MonitoringConfig
+	}
+	tests := []struct {
+		name    string
+		args    args
+		want    assert.ValueAssertionFunc // value assertion for *apm.Tracer returned by initTracer
+		wantErr assert.ErrorAssertionFunc
+	}{
+		{
+			name: "monitoring config disabled",
+			args: args{
+				agentName: "testagent",
+				version:   "1.2.3",
+				mcfg: &monitoringCfg.MonitoringConfig{
+					Enabled: false,
+				},
+			},
+			want:    assert.Nil,
+			wantErr: assert.NoError,
+		},
+		{
+			name: "monitoring config enabled but traces disabled",
+			args: args{
+				agentName: "testagent",
+				version:   "1.2.3",
+				mcfg: &monitoringCfg.MonitoringConfig{
+					Enabled:       true,
+					MonitorTraces: false,
+				},
+			},
+			want:    assert.Nil,
+			wantErr: assert.NoError,
+		},
+		{
+			name: "traces enabled, no TLS",
+			args: args{
+				agentName: "testagent",
+				version:   "1.2.3",
+				mcfg: &monitoringCfg.MonitoringConfig{
+					Enabled:       true,
+					MonitorTraces: true,
+					APM: monitoringCfg.APMConfig{
+						Environment: "unit-test",
+						APIKey:      "api-key",
+						SecretToken: "secret-token",
+						Hosts:       []string{"localhost:8888"},
+						GlobalLabels: map[string]string{
+							"k1": "v1",
+							"k2": "v2",
+						},
+						TLS:          monitoringCfg.APMTLS{},
+						SamplingRate: &tenPercentSamplingRate,
+					},
+				},
+			},
+			want:    assert.NotNil,
+			wantErr: assert.NoError,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, err := initTracer(tt.args.agentName, tt.args.version, tt.args.mcfg)
+			if got != nil {
+				t.Cleanup(func() {
+					got.Close()
+				})
+			}
+			if !tt.wantErr(t, err, fmt.Sprintf("initTracer(%v, %v, %v)", tt.args.agentName, tt.args.version, tt.args.mcfg)) {
+				return
+			}
+			tt.want(t, got, "initTracer(%v, %v, %v)", tt.args.agentName, tt.args.version, tt.args.mcfg)
+		})
+	}
+}