add tests

pkg/util/cloudproviders/network.go

@@ -58,7 +58,7 @@ func GetNetworkID(ctx context.Context) (string, error) {
 		})
 }
 
-func getVPCSubnetsForHost(ctx context.Context) ([]string, error) {
+func getVPCSubnetsForHostImpl(ctx context.Context) ([]string, error) {
 	subnets, ec2err := ec2.GetVPCSubnetsForHost(ctx)
 	if ec2err == nil {
 		return subnets, nil
@@ -69,6 +69,9 @@ func getVPCSubnetsForHost(ctx context.Context) ([]string, error) {
 	return nil, fmt.Errorf("could not detect VPC subnets: %w", errors.Join(ec2err))
 }
 
+// use a global to allow easy mocking
+var getVPCSubnetsForHost = getVPCSubnetsForHostImpl
+
 // GetVPCSubnetsForHost gets all the subnets in the VPCs this host has network interfaces for
 func GetVPCSubnetsForHost(ctx context.Context) ([]*net.IPNet, error) {
 	return cache.GetWithExpiration[[]*net.IPNet](

pkg/util/cloudproviders/network_test.go

@@ -0,0 +1,66 @@
+// Unless explicitly stated otherwise all files in this repository are licensed
+// under the Apache License Version 2.0.
+// This product includes software developed at Datadog (https://www.datadoghq.com/).
+// Copyright 2025-present Datadog, Inc.
+
+package cloudproviders
+
+import (
+	"context"
+	"errors"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+
+	"github.com/DataDog/datadog-agent/pkg/util/cache"
+)
+
+// addCleanupForSubnets clears the subnet cache after the tests.
+// otherwise, tests will interfere with each other.
+func addCleanupForSubnets(t *testing.T) {
+	t.Cleanup(func() {
+		cache.Cache.Delete(vpcSubnetsForHostCacheKey)
+	})
+}
+
+// mockGetVPCSubnetsForHostImpl replaces the implementation of getVPCSubnetsForHost with a mock
+func mockGetVPCSubnetsForHostImpl(t *testing.T, mock func(context.Context) ([]string, error)) {
+	t.Cleanup(func() { getVPCSubnetsForHost = getVPCSubnetsForHostImpl })
+	getVPCSubnetsForHost = mock
+}
+
+func TestGetVPCSubnetsForHost(t *testing.T) {
+	addCleanupForSubnets(t)
+	expectedSubnets := []string{"192.168.1.0/24", "beef::/64"}
+	mockGetVPCSubnetsForHostImpl(t, func(_ context.Context) ([]string, error) {
+		return expectedSubnets, nil
+	})
+	subnets, err := GetVPCSubnetsForHost(context.Background())
+	require.NoError(t, err)
+
+	var actualSubnets []string
+	for _, subnet := range subnets {
+		actualSubnets = append(actualSubnets, subnet.String())
+	}
+	// check that it parsed the subnets correctly
+	require.ElementsMatch(t, expectedSubnets, actualSubnets)
+}
+
+func TestGetVPCSubnetsForHostInvalid(t *testing.T) {
+	addCleanupForSubnets(t)
+	mockGetVPCSubnetsForHostImpl(t, func(_ context.Context) ([]string, error) {
+		return []string{"not a valid subnet"}, nil
+	})
+	_, err := GetVPCSubnetsForHost(context.Background())
+	require.Error(t, err)
+}
+
+func TestGetVPCSubnetsForHostError(t *testing.T) {
+	addCleanupForSubnets(t)
+	errMock := errors.New("mock error")
+	mockGetVPCSubnetsForHostImpl(t, func(_ context.Context) ([]string, error) {
+		return nil, errMock
+	})
+	_, err := GetVPCSubnetsForHost(context.Background())
+	require.ErrorIs(t, err, errMock)
+}

pkg/util/ec2/network_test.go

@@ -141,3 +141,58 @@ func TestGetInstanceIDMultipleVPC(t *testing.T) {
 	require.Error(t, err)
 	assert.Contains(t, err.Error(), "too many mac addresses returned")
 }
+
+func TestGetVPCSubnets(t *testing.T) {
+	ctx := context.Background()
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", "text/plain")
+		switch r.Method {
+		case http.MethodPut: // token request
+			io.WriteString(w, testIMDSToken)
+		case http.MethodGet: // metadata request
+			switch r.RequestURI {
+			case "/network/interfaces/macs":
+				io.WriteString(w, "00:00:00:12:34/\n")
+				io.WriteString(w, "00:00:00:56:78/")
+			case "/network/interfaces/macs/00:00:00:12:34/vpc-ipv4-cidr-blocks":
+				io.WriteString(w, "10.1.56.0/8\n")
+				io.WriteString(w, "10.1.56.1/8")
+			case "/network/interfaces/macs/00:00:00:12:34/vpc-ipv6-cidr-blocks":
+				io.WriteString(w, "2600::/64\n")
+				io.WriteString(w, "2601::/64")
+			case "/network/interfaces/macs/00:00:00:56:78/vpc-ipv4-cidr-blocks":
+				io.WriteString(w, "10.1.56.2/8\n")
+				io.WriteString(w, "10.1.56.3/8")
+			case "/network/interfaces/macs/00:00:00:56:78/vpc-ipv6-cidr-blocks":
+				io.WriteString(w, "2602::/64\n")
+				io.WriteString(w, "2603::/64")
+			default:
+				w.WriteHeader(http.StatusNotFound)
+			}
+		}
+	}))
+	defer ts.Close()
+
+	defer resetPackageVars()
+	metadataURL = ts.URL
+	tokenURL = ts.URL
+	conf := configmock.New(t)
+	conf.SetWithoutSource("ec2_metadata_timeout", 1000)
+
+	subnets, err := GetVPCSubnetsForHost(ctx)
+	assert.NoError(t, err)
+
+	expected := []string{
+		"10.1.56.0/8",
+		"10.1.56.1/8",
+		"2600::/64",
+		"2601::/64",
+		"10.1.56.2/8",
+		"10.1.56.3/8",
+		"2602::/64",
+		"2603::/64",
+	}
+
+	// elements may come back in any order
+	require.ElementsMatch(t, expected, subnets)
+}