diff --git a/.github/workflows/main.yaml b/.github/workflows/main.yaml
index 027a62bc..2e5b2526 100644
--- a/.github/workflows/main.yaml
+++ b/.github/workflows/main.yaml
@@ -12,6 +12,9 @@ jobs:
     env:
       MUGGLE_PKG_NAME: ${{ github.event.repository.name }}
       GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+      crossref_plus: ${{ secrets.CR_MD_PLUS_TOKEN }}
+      # TODO commiter email here https://github.com/subugoe/metar/issues/110
+      crossref_email: held@sub.uni-goettingen.de
     steps:
       - uses: actions/checkout@v2
       - name: Cache R Packages
diff --git a/DESCRIPTION b/DESCRIPTION
index 5a22406e..1e5331d1 100644
--- a/DESCRIPTION
+++ b/DESCRIPTION
@@ -49,10 +49,13 @@ Suggests:
     testthat,
     subugoetheme,
     shinycaas,
-    rmarkdown
+    rmarkdown,
+    bench (>= 1.1.1)
 URL: https://subugoe.github.io/metacheck, https://github.com/subugoe/metacheck
 BugReports: https://github.com/subugoe/metacheck/issues
 Remotes:
     subugoe/subugoetheme@1.1.1,
     subugoe/shinycaas@1.0.0,
+    subugoe/rcrossref@51d036808c1dc1f46cf1bad1b136e97ad213e162
     rstudio/shinyvalidate
+Config/testthat/edition: 3
diff --git a/R/test_helper.R b/R/test_helper.R
new file mode 100644
index 00000000..cd3c20ed
--- /dev/null
+++ b/R/test_helper.R
@@ -0,0 +1,3 @@
+is_valid_email <- function(x) {
+  grepl("^\\s*[A-Z0-9._%+-]+@[A-Z0-9.-]+\\.[A-Z]{2,}\\s*$", as.character(x), ignore.case=TRUE)
+}
diff --git a/tests/testthat.R b/tests/testthat.R
new file mode 100644
index 00000000..bf96ceda
--- /dev/null
+++ b/tests/testthat.R
@@ -0,0 +1,4 @@
+library(testthat)
+library(metacheck)
+
+test_check("metacheck")
diff --git a/tests/testthat/test-cr_auth.R b/tests/testthat/test-cr_auth.R
new file mode 100644
index 00000000..3c78c7d7
--- /dev/null
+++ b/tests/testthat/test-cr_auth.R
@@ -0,0 +1,22 @@
+test_that("crossref metadata is enabled", {
+  # could not capture with header response from rcrossref,
+  # so result must be inspected manually in logs
+  rcrossref::cr_abstract('10.1109/TASC.2010.2088091', verbose = TRUE)
+  expect_equal(1, 1)
+})
+
+test_that("crossref metadata plus is faster", {
+  skip("Test does not work; times are often the same.")
+  with_mdplus <- bench::bench_time(
+    rcrossref::cr_agency(sample_dois[1:10], .progress = "text")
+  )["real"]
+  withr::local_envvar(.new = c("crossref_plus" = ""))
+  without_mdplus <- bench::bench_time(
+    rcrossref::cr_agency(sample_dois[1:10], .progress = "text")
+  )["real"]
+  expect_lte(with_mdplus, without_mdplus)
+})
+
+test_that("metacheck declares polite user agent", {
+  expect_true(is_valid_email(Sys.getenv("crossref_email")))
+})