js: Use the newly extracted module system in tests

This is the main place where the module system being available
and working the same in tests as it does when k6 runs is really
important for the test itself.

js/modules/k6/experimental/tracing/module_test.go

@@ -3,7 +3,6 @@ package tracing
 import (
 	"testing"
 
-	"github.com/dop251/goja"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 	"go.k6.io/k6/js/modules/k6/http"
@@ -59,16 +58,14 @@ type testSetup struct {
 
 func newTestSetup(t *testing.T) testSetup {
 	ts := modulestest.NewRuntime(t)
-	m := new(RootModule).NewModuleInstance(ts.VU)
-
-	rt := ts.VU.Runtime()
-	require.NoError(t, rt.Set("instrumentHTTP", m.Exports().Named["instrumentHTTP"]))
-
-	export := http.New().NewModuleInstance(ts.VU).Exports().Default
-	require.NoError(t, rt.Set("require", func(module string) *goja.Object {
-		require.Equal(t, "k6/http", module)
-		return rt.ToValue(export).ToObject(rt)
-	}))
+	err := ts.SetupModuleSystem(map[string]interface{}{
+		"k6/http":                 http.New(),
+		"k6/experimental/tracing": new(RootModule),
+	}, nil)
+	require.NoError(t, err)
+
+	_, err = ts.VU.Runtime().RunString("var instrumentHTTP = require('k6/experimental/tracing').instrumentHTTP")
+	require.NoError(t, err)
 
 	return testSetup{
 		t:           t,

js/modulestest/runtime.go

@@ -3,11 +3,13 @@ package modulestest
 
 import (
 	"context"
+	"net/url"
 	"testing"
 
 	"github.com/dop251/goja"
 	"go.k6.io/k6/js/common"
 	"go.k6.io/k6/js/eventloop"
+	"go.k6.io/k6/js/modules"
 	"go.k6.io/k6/lib"
 	"go.k6.io/k6/lib/testutils"
 	"go.k6.io/k6/metrics"
@@ -55,3 +57,12 @@ func (r *Runtime) MoveToVUContext(state *lib.State) {
 	r.VU.InitEnvField = nil
 	r.VU.StateField = state
 }
+
+// SetupModuleSystem setups the modules system for the current Runtime
+// see [modules.NewModuleResolver] for the meaining of the parameters
+func (r *Runtime) SetupModuleSystem(goModules map[string]interface{}, loader modules.CJSModuleLoader) error {
+	mr := modules.NewModuleResolver(goModules, loader)
+	ms := modules.NewModuleSystem(mr, r.VU)
+	impl := modules.NewOldRequireImpl(r.VU, ms, url.URL{})
+	return r.VU.RuntimeField.Set("require", impl.Require)
+}