diff --git a/buildengine/deploy.go b/buildengine/deploy.go
index d533195e0a..ced1152336 100644
--- a/buildengine/deploy.go
+++ b/buildengine/deploy.go
@@ -26,8 +26,16 @@ type deploymentArtefact struct {
 	localPath string
 }
 
+type DeployClient interface {
+	GetArtefactDiffs(context.Context, *connect.Request[ftlv1.GetArtefactDiffsRequest]) (*connect.Response[ftlv1.GetArtefactDiffsResponse], error)
+	UploadArtefact(context.Context, *connect.Request[ftlv1.UploadArtefactRequest]) (*connect.Response[ftlv1.UploadArtefactResponse], error)
+	CreateDeployment(context.Context, *connect.Request[ftlv1.CreateDeploymentRequest]) (*connect.Response[ftlv1.CreateDeploymentResponse], error)
+	ReplaceDeploy(context.Context, *connect.Request[ftlv1.ReplaceDeployRequest]) (*connect.Response[ftlv1.ReplaceDeployResponse], error)
+	Status(context.Context, *connect.Request[ftlv1.StatusRequest]) (*connect.Response[ftlv1.StatusResponse], error)
+}
+
 // Deploy a module to the FTL controller with the given number of replicas. Optionally wait for the deployment to become ready.
-func Deploy(ctx context.Context, module Module, replicas int32, waitForDeployOnline bool, client ftlv1connect.ControllerServiceClient) error {
+func Deploy(ctx context.Context, module Module, replicas int32, waitForDeployOnline bool, client DeployClient) error {
 	logger := log.FromContext(ctx).Scope(module.Module)
 	ctx = log.ContextWithLogger(ctx, logger)
 	logger.Infof("Deploying module")
@@ -221,7 +229,7 @@ func relToCWD(path string) string {
 	return rel
 }
 
-func checkReadiness(ctx context.Context, client ftlv1connect.ControllerServiceClient, deploymentName string, replicas int32) error {
+func checkReadiness(ctx context.Context, client DeployClient, deploymentName string, replicas int32) error {
 	ticker := time.NewTicker(time.Second)
 	defer ticker.Stop()
 
diff --git a/buildengine/deploy_test.go b/buildengine/deploy_test.go
new file mode 100644
index 0000000000..e70f81f3e3
--- /dev/null
+++ b/buildengine/deploy_test.go
@@ -0,0 +1,84 @@
+package buildengine
+
+import (
+	"context"
+	"os"
+	"testing"
+
+	"connectrpc.com/connect"
+	ftlv1 "github.com/TBD54566975/ftl/backend/protos/xyz/block/ftl/v1"
+	"github.com/TBD54566975/ftl/backend/schema"
+	"github.com/TBD54566975/ftl/internal/log"
+	"github.com/TBD54566975/ftl/internal/sha256"
+	"github.com/alecthomas/assert/v2"
+)
+
+type mockDeployClient struct {
+	MissingDigests []string
+	DeploymentName string
+}
+
+func (m *mockDeployClient) GetArtefactDiffs(context.Context, *connect.Request[ftlv1.GetArtefactDiffsRequest]) (*connect.Response[ftlv1.GetArtefactDiffsResponse], error) {
+	return connect.NewResponse(&ftlv1.GetArtefactDiffsResponse{
+		MissingDigests: m.MissingDigests,
+	}), nil
+}
+
+func (m *mockDeployClient) UploadArtefact(ctx context.Context, req *connect.Request[ftlv1.UploadArtefactRequest]) (*connect.Response[ftlv1.UploadArtefactResponse], error) {
+	sha256digest := sha256.Sum(req.Msg.Content)
+	return connect.NewResponse(&ftlv1.UploadArtefactResponse{Digest: sha256digest[:]}), nil
+}
+
+func (m *mockDeployClient) CreateDeployment(context.Context, *connect.Request[ftlv1.CreateDeploymentRequest]) (*connect.Response[ftlv1.CreateDeploymentResponse], error) {
+	return connect.NewResponse(&ftlv1.CreateDeploymentResponse{DeploymentName: m.DeploymentName}), nil
+}
+
+func (m *mockDeployClient) ReplaceDeploy(context.Context, *connect.Request[ftlv1.ReplaceDeployRequest]) (*connect.Response[ftlv1.ReplaceDeployResponse], error) {
+	return nil, nil
+}
+
+func (m *mockDeployClient) Status(context.Context, *connect.Request[ftlv1.StatusRequest]) (*connect.Response[ftlv1.StatusResponse], error) {
+	resp := &ftlv1.StatusResponse{
+		Deployments: []*ftlv1.StatusResponse_Deployment{
+			{Key: m.DeploymentName, Replicas: 1},
+		},
+	}
+	return connect.NewResponse(resp), nil
+}
+
+func TestDeploy(t *testing.T) {
+	sch := &schema.Schema{
+		Modules: []*schema.Module{
+			schema.Builtins(),
+			{Name: "another", Decls: []schema.Decl{
+				&schema.Data{Name: "EchoRequest"},
+				&schema.Data{Name: "EchoResponse"},
+				&schema.Verb{
+					Name:     "echo",
+					Request:  &schema.DataRef{Name: "EchoRequest"},
+					Response: &schema.DataRef{Name: "EchoResponse"},
+				},
+			}},
+		},
+	}
+	ctx := log.ContextWithLogger(context.Background(), log.Configure(os.Stderr, log.Config{}))
+
+	modulePath := "testdata/modules/another"
+	module, err := LoadModule(ctx, modulePath)
+	assert.NoError(t, err)
+
+	// Build first to make sure the files are there.
+	err = Build(ctx, sch, module)
+	assert.NoError(t, err)
+
+	sum, err := sha256.SumFile(modulePath + "/_ftl/main")
+	assert.NoError(t, err)
+
+	client := &mockDeployClient{
+		MissingDigests: []string{sum.String()},
+		DeploymentName: "test-deployment",
+	}
+
+	err = Deploy(ctx, module, int32(1), true, client)
+	assert.NoError(t, err)
+}