Fix panic on metricbeat test modules

CHANGELOG.next.asciidoc

@@ -206,6 +206,7 @@ field. You can revert this change by configuring tags for the module and omittin
 - Remove specific win32 api errors from events in perfmon. {issue}18292[18292] {pull}18361[18361]
 - Fix application_pool metricset after pdh changes. {pull}18477[18477]
 - Fix tags_filter for cloudwatch metricset in aws. {pull}18524[18524]
+- Fix panic on `metricbeat test modules` when modules are configured in `metricbeat.modules`. {issue}18789[18789] {pull}18797[18797]
 - Fix getting gcp compute instance metadata with partial zone/region in config. {pull}18757[18757]
 - Add missing network.sent_packets_count metric into compute metricset in googlecloud module. {pull}18802[18802]
 

metricbeat/cmd/test/modules.go

@@ -25,6 +25,7 @@ import (
 
 	"github.com/elastic/beats/v7/libbeat/beat"
 	"github.com/elastic/beats/v7/libbeat/cmd/instance"
+	"github.com/elastic/beats/v7/libbeat/publisher/pipeline"
 	"github.com/elastic/beats/v7/libbeat/testing"
 	"github.com/elastic/beats/v7/metricbeat/beater"
 )
@@ -49,6 +50,8 @@ func GenTestModulesCmd(name, beatVersion string, create beat.Creator) *cobra.Com
 				os.Exit(1)
 			}
 
+			// A publisher is needed for modules that add their own pipelines
+			b.Beat.Publisher = newPublisher()
 			mb, err := create(&b.Beat, b.Beat.BeatConfig)
 			if err != nil {
 				fmt.Fprintf(os.Stderr, "Error initializing metricbeat: %s\n", err)
@@ -78,3 +81,17 @@ func GenTestModulesCmd(name, beatVersion string, create beat.Creator) *cobra.Com
 		},
 	}
 }
+
+type publisher struct {
+	beat.PipelineConnector
+}
+
+// newPublisher returns a functional publisher that does nothing.
+func newPublisher() *publisher {
+	return &publisher{pipeline.NewNilPipeline()}
+}
+
+// SetACKHandler is a dummy implementation of the ack handler for the test publisher.
+func (*publisher) SetACKHandler(beat.PipelineACKHandler) error {
+	return nil
+}

metricbeat/mb/module/configuration.go

@@ -30,7 +30,7 @@ func ConfiguredModules(modulesData []*common.Config, configModulesData *common.C
 	var modules []*Wrapper
 
 	for _, moduleCfg := range modulesData {
-		module, err := NewWrapper(moduleCfg, mb.Registry, nil)
+		module, err := NewWrapper(moduleCfg, mb.Registry, moduleOptions...)
 		if err != nil {
 			return nil, err
 		}

metricbeat/tests/system/test_cmd.py

@@ -124,6 +124,21 @@ def test_modules_test(self):
         assert self.log_contains("cpu...OK")
         assert self.log_contains("memory...OK")
 
+    def test_modules_test_with_module_in_main_config(self):
+        self.render_config_template(reload=False, modules=[{
+            "name": "system",
+            "metricsets": ["cpu", "memory"],
+            "period": "10s",
+        }])
+
+        exit_code = self.run_beat(
+            logging_args=None,
+            extra_args=["test", "modules"])
+
+        assert exit_code == 0
+        assert self.log_contains("cpu...OK")
+        assert self.log_contains("memory...OK")
+
     def test_modules_test_error(self):
         """
         Test test modules command with an error result