add test

Author: teunbrand

tests/testthat/_snaps/theme.md

@@ -40,6 +40,19 @@
 
     The `blablabla` theme element must be a <element_text> object.
 
+---
+
+    `element_tree` must have names.
+
+---
+
+    `element_tree` must have elements constructed with `el_def()`.
+    i Invalid structure: "foo"
+
+---
+
+    Invalid parent in `element_tree`: "foo".
+
 # Theme elements are checked during build
 
     `plot.title.position` must be one of "panel" or "plot", not "test".

tests/testthat/test-theme.R

@@ -312,6 +312,17 @@ test_that("element tree can be modified", {
   p1 <- ggplot() + theme(blablabla = element_line())
   expect_snapshot_error(ggplotGrob(p1))
 
+  # Expect errors for invalid element trees
+  expect_snapshot_error(
+    register_theme_elements(element_tree = list(el_def("rect"), el_def("line")))
+  )
+  expect_snapshot_error(
+    register_theme_elements(element_tree = list(foo = "bar"))
+  )
+  expect_snapshot_error(
+    register_theme_elements(element_tree = list(foo = el_def(inherit = "foo")))
+  )
+
   # inheritance and final calculation of novel element works
   final_theme <- ggplot2:::plot_theme(p, theme_gray())
   e1 <- calc_element("blablabla", final_theme)