diff --git a/tests/testthat/test-common-item-mapping.R b/tests/testthat/test-common-item-mapping.R
new file mode 100644
index 00000000..fe231317
--- /dev/null
+++ b/tests/testthat/test-common-item-mapping.R
@@ -0,0 +1,122 @@
+test_that("autoFIPC fails fast when common-item mappings do not resolve", {
+  new_data <- data.frame(
+    new_anchor = c(0, 1, 0, 1),
+    new_unique = c(1, 0, 1, 0),
+    check.names = FALSE
+  )
+  old_data <- data.frame(
+    old_anchor = c(0, 1, 1, 0),
+    old_unique = c(1, 0, 0, 1),
+    check.names = FALSE
+  )
+
+  expect_error(
+    autoFIPC(
+      newformXData = new_data,
+      oldformYData = old_data,
+      newformCommonItemNames = "missing_new_anchor",
+      oldformCommonItemNames = "old_anchor",
+      itemtype = "2PL",
+      confirmCommonItems = FALSE
+    ),
+    "newformCommonItemNames.*not present"
+  )
+
+  expect_error(
+    autoFIPC(
+      newformXData = new_data,
+      oldformYData = old_data,
+      newformCommonItemNames = "new_anchor",
+      oldformCommonItemNames = "missing_old_anchor",
+      itemtype = "2PL",
+      confirmCommonItems = FALSE
+    ),
+    "oldformCommonItemNames.*not present"
+  )
+})
+
+test_that("autoFIPC rejects ambiguous common-item mappings before confirmation", {
+  new_data <- data.frame(
+    new_anchor = c(0, 1, 0, 1),
+    new_unique = c(1, 0, 1, 0),
+    check.names = FALSE
+  )
+  old_data <- data.frame(
+    old_anchor = c(0, 1, 1, 0),
+    old_unique = c(1, 0, 0, 1),
+    check.names = FALSE
+  )
+
+  expect_error(
+    autoFIPC(
+      newformXData = new_data,
+      oldformYData = old_data,
+      newformCommonItemNames = c("new_anchor", "new_anchor"),
+      oldformCommonItemNames = c("old_anchor", "old_unique"),
+      itemtype = "2PL",
+      confirmCommonItems = FALSE
+    ),
+    "newformCommonItemNames.*unique"
+  )
+
+  expect_error(
+    autoFIPC(
+      newformXData = new_data,
+      oldformYData = old_data,
+      newformCommonItemNames = c("new_anchor", "new_unique"),
+      oldformCommonItemNames = c("old_anchor", "old_anchor"),
+      itemtype = "2PL",
+      confirmCommonItems = FALSE
+    ),
+    "oldformCommonItemNames.*unique"
+  )
+
+  expect_error(
+    autoFIPC(
+      newformXData = new_data,
+      oldformYData = old_data,
+      newformCommonItemNames = NA_character_,
+      oldformCommonItemNames = "old_anchor",
+      itemtype = "2PL",
+      confirmCommonItems = FALSE
+    ),
+    "newformCommonItemNames.*non-missing"
+  )
+
+  expect_error(
+    autoFIPC(
+      newformXData = new_data,
+      oldformYData = old_data,
+      newformCommonItemNames = "",
+      oldformCommonItemNames = "old_anchor",
+      itemtype = "2PL",
+      confirmCommonItems = FALSE
+    ),
+    "newformCommonItemNames.*non-empty"
+  )
+})
+
+test_that("factor common-item names preserve the documented accepted type", {
+  new_data <- data.frame(
+    new_anchor = c(0, 1, 0, 1),
+    new_unique = c(1, 0, 1, 0),
+    check.names = FALSE
+  )
+  old_data <- data.frame(
+    old_anchor = c(0, 1, 1, 0),
+    old_unique = c(1, 0, 0, 1),
+    check.names = FALSE
+  )
+
+  expect_error(
+    autoFIPC(
+      newformXData = new_data,
+      oldformYData = old_data,
+      newformCommonItemNames = factor("new_anchor"),
+      oldformCommonItemNames = factor("old_anchor"),
+      itemtype = "2PL",
+      confirmCommonItems = FALSE
+    ),
+    "Please write down pairs correctly"
+  )
+})