test(agentcompat): capture FD observations in process samples

Co-authored-by: naiba/CloudCode <hi+cloudcode@nai.ba>

integration/agentcompat/internal/process/sampler_fd_observations_test.go

@@ -0,0 +1,45 @@
+//go:build linux
+
+package process
+
+import (
+	"context"
+	"encoding/json"
+	"os"
+	"testing"
+	"time"
+)
+
+func TestSampleProcessWithFDObservations_CapturesEverySuccessfulNonStdioReadlink(t *testing.T) {
+	// Given / When
+	sample, err := SampleProcessWithFDObservations(os.Getpid())
+
+	// Then
+	requireNoError(t, err)
+	if len(sample.FDObservations) != sample.NonStdioFDCount {
+		t.Fatalf("FD observations = %d, non-stdio FD count = %d", len(sample.FDObservations), sample.NonStdioFDCount)
+	}
+	if sample.SampledAt.IsZero() {
+		t.Fatal("sampled at is zero")
+	}
+	encoded, err := json.Marshal(sample)
+	requireNoError(t, err)
+	var evidence map[string]json.RawMessage
+	requireNoError(t, json.Unmarshal(encoded, &evidence))
+	if _, exists := evidence["sampled_at"]; exists {
+		t.Fatalf("sampled_at leaked into evidence JSON: %s", encoded)
+	}
+}
+
+func TestSampleWindowWithFDObservations_RecordsCompletionTimeForEverySample(t *testing.T) {
+	// Given / When
+	window, err := SampleWindow(context.Background(), WindowSpec{PID: os.Getpid(), Interval: time.Nanosecond, CaptureFDObservations: true})
+
+	// Then
+	requireNoError(t, err)
+	for index, sample := range window.Samples {
+		if sample.SampledAt.IsZero() {
+			t.Fatalf("sample %d sampled at is zero", index+1)
+		}
+	}
+}