Demonstrate a WAI FPDFPage_RemoveObject() failure case

Show that FPDFPage_RemoveObject() does not work for page objects which
are not directly contained by the page.

Bug: pdfium:2073
Change-Id: Id73008033f998bcf8ece0e3165c37d5a9a7b58ef
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/112573
Reviewed-by: Nigi <nigi@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>
diff --git a/fpdfsdk/fpdf_edit_embeddertest.cpp b/fpdfsdk/fpdf_edit_embeddertest.cpp
index b4d09de..4535801 100644
--- a/fpdfsdk/fpdf_edit_embeddertest.cpp
+++ b/fpdfsdk/fpdf_edit_embeddertest.cpp
@@ -3017,6 +3017,12 @@
   // FPDFPageObj_GetMatrix() negative testing for forms.
   EXPECT_FALSE(FPDFPageObj_GetMatrix(form, nullptr));
 
+  // Show that FPDFPage_RemoveObject() cannot remove page objects from within
+  // `form`. This is working as intended, as FPDFPage_RemoveObject() only works
+  // for page object within `page`.
+  EXPECT_FALSE(FPDFPage_RemoveObject(page, text1));
+  EXPECT_FALSE(FPDFPage_RemoveObject(page, text2));
+
   UnloadPage(page);
 }