diff --git a/inst/tinytest/test-lfmcmc.R b/inst/tinytest/test-lfmcmc.R
index 42835df..aa89b48 100644
--- a/inst/tinytest/test-lfmcmc.R
+++ b/inst/tinytest/test-lfmcmc.R
@@ -19,6 +19,7 @@ expect_silent(lfmcmc_model <- LFMCMC(model_sir))
 
 # Check initialization
 expect_inherits(lfmcmc_model, "epiworld_lfmcmc")
+expect_length(class(lfmcmc_model), 1)
 
 # Extract observed data from the model
 obs_data <- unname(as.integer(get_today_total(model_sir)))
diff --git a/inst/tinytest/test-sir.R b/inst/tinytest/test-sir.R
index 4913730..c9bcd46 100644
--- a/inst/tinytest/test-sir.R
+++ b/inst/tinytest/test-sir.R
@@ -29,6 +29,7 @@ expect_silent(sir_0 <- ModelSIR(
 # Check model initialization
 expect_inherits(sir_0, "epiworld_sir")
 expect_inherits(sir_0, "epiworld_model")
+expect_length(class(sir_0), 2)
 expect_silent(agents_smallworld(
   sir_0,
   n = 50000,
diff --git a/inst/tinytest/test-sirconn.R b/inst/tinytest/test-sirconn.R
index b026c4f..0370284 100644
--- a/inst/tinytest/test-sirconn.R
+++ b/inst/tinytest/test-sirconn.R
@@ -36,6 +36,7 @@ expect_silent(sirconn_0 <- ModelSIRCONN(
 # Check model initialization
 expect_inherits(sirconn_0, "epiworld_sirconn")
 expect_inherits(sirconn_0, "epiworld_model")
+expect_length(class(sirconn_0), 2)
 
 # Check model run with queuing -------------------------------------------------
 expect_silent(verbose_off(sirconn_0))
diff --git a/inst/tinytest/test-sird.R b/inst/tinytest/test-sird.R
index 2beddd2..4e20166 100644
--- a/inst/tinytest/test-sird.R
+++ b/inst/tinytest/test-sird.R
@@ -12,6 +12,7 @@ expect_silent(sird_0 <- ModelSIRD(
 # Check model initialization
 expect_inherits(sird_0, "epiworld_sird")
 expect_inherits(sird_0, "epiworld_model")
+expect_length(class(sird_0), 2)
 expect_silent(agents_smallworld(
   sird_0,
   n = 10000,
diff --git a/inst/tinytest/test-sis.R b/inst/tinytest/test-sis.R
index 1b57afa..b4c3b62 100644
--- a/inst/tinytest/test-sis.R
+++ b/inst/tinytest/test-sis.R
@@ -11,6 +11,7 @@ expect_silent(sis_0 <- ModelSIS(
 # Check model initialization
 expect_inherits(sis_0, "epiworld_sis")
 expect_inherits(sis_0, "epiworld_model")
+expect_length(class(sis_0), 2)
 expect_silent(agents_smallworld(
   sis_0,
   n = 2000,