test(18-03): add failing tests for SNMPCollector interface and edge cases

- Compile-time Collector interface assertion
- Collect returns error with nil SNMPProfileID
- Collect returns error with unknown profile ID
- NewSNMPCollector returns initialized struct

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

poller/internal/snmp/collector_test.go

@@ -0,0 +1,67 @@
+package snmp
+
+import (
+	"context"
+	"testing"
+
+	"github.com/staack/the-other-dude/poller/internal/bus"
+	poller "github.com/staack/the-other-dude/poller/internal/poller"
+	"github.com/staack/the-other-dude/poller/internal/store"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+// TestSNMPCollectorImplementsCollector is a compile-time interface assertion
+// that SNMPCollector satisfies the poller.Collector interface.
+func TestSNMPCollectorImplementsCollector(t *testing.T) {
+	// This test verifies the compile-time assertion in collector.go.
+	// If this compiles, SNMPCollector satisfies the Collector interface.
+	var _ poller.Collector = (*SNMPCollector)(nil)
+}
+
+// TestSNMPCollectorCollect_NilProfileID verifies that Collect returns an error
+// when the device has no SNMPProfileID set.
+func TestSNMPCollectorCollect_NilProfileID(t *testing.T) {
+	collector := NewSNMPCollector(nil, nil, nil, DefaultSNMPConfig())
+	dev := store.Device{
+		ID:            "test-device-001",
+		TenantID:      "test-tenant-001",
+		DeviceType:    "snmp",
+		SNMPProfileID: nil, // no profile
+	}
+
+	err := collector.Collect(context.Background(), dev, &bus.Publisher{})
+	require.Error(t, err)
+	assert.Contains(t, err.Error(), "no SNMP profile")
+}
+
+// TestSNMPCollectorCollect_UnknownProfileID verifies that Collect returns an error
+// when the device's profile ID is not found in the ProfileCache.
+func TestSNMPCollectorCollect_UnknownProfileID(t *testing.T) {
+	// Create a ProfileCache with no loaded profiles.
+	profiles := &ProfileCache{
+		profiles: make(map[string]*CompiledProfile),
+	}
+
+	collector := NewSNMPCollector(profiles, nil, nil, DefaultSNMPConfig())
+	unknownID := "nonexistent-profile-uuid"
+	dev := store.Device{
+		ID:            "test-device-002",
+		TenantID:      "test-tenant-001",
+		DeviceType:    "snmp",
+		SNMPProfileID: &unknownID,
+	}
+
+	err := collector.Collect(context.Background(), dev, &bus.Publisher{})
+	require.Error(t, err)
+	assert.Contains(t, err.Error(), "profile not found")
+}
+
+// TestSNMPCollectorNewCreatesInstance verifies NewSNMPCollector returns a properly
+// initialized struct with all dependencies set.
+func TestSNMPCollectorNewCreatesInstance(t *testing.T) {
+	cfg := DefaultSNMPConfig()
+	collector := NewSNMPCollector(nil, nil, nil, cfg)
+	require.NotNil(t, collector)
+	assert.Equal(t, cfg.MaxRepetitions, collector.cfg.MaxRepetitions)
+}