chore: minor refactor of the prometheus module

pkg/gotenberg/mocks.go

@@ -109,6 +109,15 @@ func (provider *LoggerProviderMock) Logger(mod Module) (*zap.Logger, error) {
 	return provider.LoggerMock(mod)
 }
 
+// MetricsProviderMock is a mock for the [MetricsProvider] interface.
+type MetricsProviderMock struct {
+	MetricsMock func() ([]Metric, error)
+}
+
+func (provider *MetricsProviderMock) Metrics() ([]Metric, error) {
+	return provider.MetricsMock()
+}
+
 // Interface guards.
 var (
 	_ Module            = (*ModuleMock)(nil)
@@ -118,4 +127,5 @@ var (
 	_ Process           = (*ProcessMock)(nil)
 	_ ProcessSupervisor = (*ProcessSupervisorMock)(nil)
 	_ LoggerProvider    = (*LoggerProviderMock)(nil)
+	_ MetricsProvider   = (*MetricsProviderMock)(nil)
 )

pkg/gotenberg/mocks_test.go

@@ -162,3 +162,16 @@ func TestLoggerProviderMock(t *testing.T) {
 		t.Errorf("expected no error from LoggerProviderMock.Logger, but got: %v", err)
 	}
 }
+
+func TestMetricsProviderMock(t *testing.T) {
+	mock := &MetricsProviderMock{
+		MetricsMock: func() ([]Metric, error) {
+			return nil, nil
+		},
+	}
+
+	_, err := mock.Metrics()
+	if err != nil {
+		t.Errorf("expected no error from MetricsProviderMock.Metrics, but got: %v", err)
+	}
+}