diff --git a/tests/testthat/test-common-affixes.R b/tests/testthat/test-common-affixes.R
new file mode 100644
index 0000000..0314864
--- /dev/null
+++ b/tests/testthat/test-common-affixes.R
@@ -0,0 +1,59 @@
+lcp <- RKorAPClient:::longestCommonPrefixLength
+lcs <- RKorAPClient:::longestCommonSuffixLength
+
+test_that("longestCommonPrefixLength counts the shared prefix", {
+  expect_equal(lcp(c("abc", "abd")), 2)
+  expect_equal(lcp(c("abc", "abc")), 3)
+  expect_equal(lcp(c("xyz", "abc")), 0)
+  expect_equal(lcp(c("aaa", "aa", "a")), 1)
+  expect_equal(lcp(c("prefix_A_suffix", "prefix_B_suffix")), 7)
+  expect_equal(lcp(c("üöä-test", "üöä-rest")), 4)
+})
+
+test_that("longestCommonSuffixLength counts the shared suffix", {
+  expect_equal(lcs(c("abc", "dbc")), 2)
+  expect_equal(lcs(c("abc", "abc")), 3)
+  expect_equal(lcs(c("xyz", "abc")), 0)
+  expect_equal(lcs(c("aaa", "aa", "a")), 1)
+  expect_equal(lcs(c("prefix_A_suffix", "prefix_B_suffix")), 7)
+  expect_equal(lcs(c("abc-üöä", "xyz-üöä")), 4)
+})
+
+test_that("empty vectors, empty strings and single strings behave as before", {
+  # a single string is its own prefix and suffix, as in the PTXQC functions
+  # these replace
+  expect_equal(lcp(character(0)), 0)
+  expect_equal(lcs(character(0)), 0)
+  expect_equal(lcp("single"), 6)
+  expect_equal(lcs("single"), 6)
+  expect_equal(lcp(c("", "")), 0)
+  expect_equal(lcs(c("", "")), 0)
+  expect_equal(lcp(c("abc", "")), 0)
+  expect_equal(lcs(c("", "abc")), 0)
+})
+
+test_that("queryStringToLabel clips common prefixes and suffixes", {
+  expect_equal(
+    queryStringToLabel(paste("textType = /Zeit.*/ & pubDate in", 2010:2019)),
+    as.character(2010:2019)
+  )
+  expect_equal(
+    queryStringToLabel(c("[marmot/m=mood:subj]", "[marmot/m=mood:ind]")),
+    c("subj", "ind")
+  )
+  expect_equal(
+    queryStringToLabel(c("wegen dem [tt/p=NN]", "wegen des [tt/p=NN]")),
+    c("dem", "des")
+  )
+})
+
+test_that("queryStringToLabel honours pubDateOnly and excludePubDate", {
+  vc <- paste("textType = /Zeit.*/ & pubDate in", 2010:2012)
+  expect_equal(queryStringToLabel(vc, pubDateOnly = TRUE), as.character(2010:2012))
+  expect_equal(
+    queryStringToLabel(c("textDomain = /Wirtschaft.*/ & pubDate in 2010",
+                         "textDomain != /Wirtschaft.*/ & pubDate in 2010"),
+                       excludePubDate = TRUE),
+    c("=", "!=")
+  )
+})