Add missing variable in templates regarding toc (#127)

Related to #123 and alignement with `html_document()` behavior
diff --git a/tests/testthat/test-revealjs_presentation.R b/tests/testthat/test-revealjs_presentation.R
new file mode 100644
index 0000000..ade1c9a
--- /dev/null
+++ b/tests/testthat/test-revealjs_presentation.R
@@ -0,0 +1,20 @@
+test_that("toc argument works", {
+  skip_if_not_pandoc()
+  skip_if_not_installed("xml2")
+  rmd <- local_temp_draft()
+  html <- .render_and_read(
+    rmd,
+    output_options = list(
+      toc = TRUE,
+      pandoc_args = c(pandoc_variable_arg("toc-title", "TOC"))
+    )
+  )
+  toc <- xml2::xml_find_all(html, "//section[@id='TOC']")
+  expect_length(toc, 1)
+  expect_equal(
+    xml2::xml_text(
+      xml2::xml_find_all(toc, "./nav/*[contains(@id, 'toc-title')]")
+    ),
+    "TOC"
+  )
+})