add test

Author: teunbrand

tests/testthat/_snaps/layer.md

@@ -47,6 +47,11 @@
 
     Ignoring empty aesthetics: `fill` and `shape`.
 
+# aesthetics defined twice create warning
+
+    The size aesthetic is defined twice: once in `mapping` and once as a static aesthetic.
+    i The static aesthetic overrules the mapped aesthetic.
+
 # invalid aesthetics throws errors
 
     Problem while computing aesthetics.

tests/testthat/test-layer.R

@@ -33,6 +33,10 @@ test_that("empty aesthetics create warning", {
   expect_snapshot_warning(ggplot_build(p))
 })
 
+test_that("aesthetics defined twice create warning", {
+  expect_snapshot_warning(geom_point(aes(size = foo), size = 12))
+})
+
 test_that("invalid aesthetics throws errors", {
   # We want to test error and ignore the scale search message
   suppressMessages({