diff --git a/tests/testthat/test-incidence-cancer.R b/tests/testthat/test-incidence-cancer.R
index 4ee1971..4c0525b 100644
--- a/tests/testthat/test-incidence-cancer.R
+++ b/tests/testthat/test-incidence-cancer.R
@@ -108,6 +108,20 @@ test_that("incidence_cancer has correct number of columns", {
   expect_equal(ncol(df2), expected_columns2)
 })
 
+#test error handling
+test_that("incidence_cancer handles invalid cancer parameters", {
+  expect_error(
+    incidence_cancer("wa", "county", "all cancer sites", "black (non-hispanic)", 
+                     "both sexes", "ages 65+", "late stage (regional & distant)"),
+    "For this cancer type, stage must be all stages"
+  )
+  expect_error(
+    incidence_cancer("ca", "hsa", "prostate", "all races (includes hispanic)", "both sexes", 
+                     "ages 50+", "all stages"),
+    "For prostate cancer, sex must be males."
+  )
+})
+
 # parameter
 test_that("incidence_cancer has correct parameters", {
   expect_error(incidence_cancer())
diff --git a/tests/testthat/test-mortality-cancer.R b/tests/testthat/test-mortality-cancer.R
index df1a9bd..67cf033 100644
--- a/tests/testthat/test-mortality-cancer.R
+++ b/tests/testthat/test-mortality-cancer.R
@@ -105,7 +105,23 @@ test_that("mortality_cancer has correct number of columns", {
   expect_equal(ncol(df), expected_columns)
 })
 
-# parameter
+#test error handling
+test_that("mortality_cancer handles invalid cancer parameters", {
+  expect_error(
+    mortality_cancer(area="wa", areatype="county", cancer="ovary", 
+                     race="all races (includes hispanic)", 
+                     sex="both sexes", age="ages 50+"),
+    "For this cancer type, sex must be females"
+  )
+  expect_error(
+    mortality_cancer("usa", "state", "prostate", "all races (includes hispanic)", 
+                     "both sexes", "ages 50+"),
+    "For prostate cancer, sex must be males."
+  )
+})
+
+#parameter
 test_that("mortality_cancer has correct parameters", {
   expect_error(mortality_cancer())
 })
+