diff --git a/tests/testthat/test-korapconnection-signature.R b/tests/testthat/test-korapconnection-signature.R
new file mode 100644
index 0000000..e8356fe
--- /dev/null
+++ b/tests/testthat/test-korapconnection-signature.R
@@ -0,0 +1,96 @@
+withOfflineKorAPEnv <- function(code, verboseEnv = NA_character_) {
+  oldUrl <- Sys.getenv("KORAP_URL", unset = NA_character_)
+  oldVerbose <- Sys.getenv("KORAP_VERBOSE", unset = NA_character_)
+  on.exit(
+    {
+      if (is.na(oldUrl)) Sys.unsetenv("KORAP_URL") else Sys.setenv(KORAP_URL = oldUrl)
+      if (is.na(oldVerbose)) {
+        Sys.unsetenv("KORAP_VERBOSE")
+      } else {
+        Sys.setenv(KORAP_VERBOSE = oldVerbose)
+      }
+    },
+    add = TRUE
+  )
+  Sys.setenv(KORAP_URL = "https://example.invalid/")
+  if (is.na(verboseEnv)) Sys.unsetenv("KORAP_VERBOSE") else Sys.setenv(KORAP_VERBOSE = verboseEnv)
+  force(code)
+}
+
+test_that("the documented KorAPConnection() defaults are the ones actually used", {
+  # KorAPConnection() only forwards the arguments that were supplied, so its
+  # own defaults are never evaluated. They mirror those of the initialize
+  # method to document them, and this test makes sure that the two cannot
+  # drift apart silently.
+  withOfflineKorAPEnv({
+    kco <- KorAPConnection(accessToken = NULL)
+    documented <- formals(KorAPConnection)
+
+    # accessToken (keyring), apiUrl (derived) and authorizationSupported
+    # (answered by the server) are covered by the tests below instead
+    for (parameter in c(
+      "KorAPUrl", "apiVersion", "oauthClient", "oauthScope",
+      "userAgent", "timeout", "verbose", "cache"
+    )) {
+      expect_equal(
+        slot(kco, parameter),
+        eval(documented[[parameter]]),
+        info = parameter
+      )
+    }
+  })
+})
+
+test_that("KorAPConnection() forwards only the arguments that were supplied", {
+  # `missing()` based overrides in the initialize method must keep working
+  withOfflineKorAPEnv(
+    {
+      expect_true(KorAPConnection(accessToken = NULL)@verbose)
+      # an explicitly passed verbose argument still wins over the env var
+      expect_false(KorAPConnection(accessToken = NULL, verbose = FALSE)@verbose)
+    },
+    verboseEnv = "true"
+  )
+})
+
+test_that("KorAPConnection() derives apiUrl unless it is given explicitly", {
+  kco <- KorAPConnection(KorAPUrl = "https://example.invalid/", accessToken = NULL)
+  expect_equal(kco@apiUrl, "https://example.invalid/api/v1.0/")
+
+  kco <- KorAPConnection(
+    KorAPUrl = "https://example.invalid/",
+    apiUrl = "https://other.invalid/api/",
+    accessToken = NULL
+  )
+  expect_equal(kco@apiUrl, "https://other.invalid/api/")
+})
+
+test_that("KorAPConnection objects can still be created with new()", {
+  kco <- methods::new(
+    "KorAPConnection",
+    KorAPUrl = "https://example.invalid/",
+    apiUrl = "https://example.invalid/api/v1.0/",
+    accessToken = NULL,
+    verbose = FALSE
+  )
+  expect_s4_class(kco, "KorAPConnection")
+  expect_equal(kco@apiUrl, "https://example.invalid/api/v1.0/")
+})
+
+test_that("defaultKorAPUrl() honours KORAP_URL", {
+  old <- Sys.getenv("KORAP_URL", unset = NA_character_)
+  on.exit(
+    if (is.na(old)) Sys.unsetenv("KORAP_URL") else Sys.setenv(KORAP_URL = old),
+    add = TRUE
+  )
+
+  Sys.setenv(KORAP_URL = "https://example.invalid/")
+  expect_equal(defaultKorAPUrl(), "https://example.invalid/")
+
+  # an empty KORAP_URL counts as unset
+  Sys.setenv(KORAP_URL = "")
+  expect_equal(defaultKorAPUrl(), "https://korap.ids-mannheim.de/")
+
+  Sys.unsetenv("KORAP_URL")
+  expect_equal(defaultKorAPUrl(), "https://korap.ids-mannheim.de/")
+})