patch 8.2.0401: not enough test coverage for evalvars.c

Problem:    Not enough test coverage for evalvars.c.
Solution:   Add more tests. (Yegappan Lakshmanan, closes #5804)
diff --git a/src/testdir/test_const.vim b/src/testdir/test_const.vim
index 7f95091..a0f919e 100644
--- a/src/testdir/test_const.vim
+++ b/src/testdir/test_const.vim
@@ -251,6 +251,14 @@
     call assert_fails('const &filetype = "vim"', 'E996:')
     call assert_fails('const &l:filetype = "vim"', 'E996:')
     call assert_fails('const &g:encoding = "utf-8"', 'E996:')
+
+    call assert_fails('const [a, $CONST_FOO] = [369, "abc"]', 'E996:')
+    call assert_equal(369, a)
+    call assert_equal(v:null, getenv("CONST_FOO"))
+
+    call assert_fails('const [b; $CONST_FOO] = [246, 2, "abc"]', 'E996:')
+    call assert_equal(246, b)
+    call assert_equal(v:null, getenv("CONST_FOO"))
 endfunc
 
 func Test_const_with_eval_name()
@@ -276,3 +284,5 @@
     let d['bar'] = 'hello'
     let d.foo = 44
 endfunc
+
+" vim: shiftwidth=2 sts=2 expandtab