Test expansion syntax errors.

If there is a better way to do stuff that will stop execution than
fish -c for our tests, please let me know.

tests/expansion.err

@@ -25,3 +25,17 @@ echo $$paren
 
 ####################
 # Test path variables
+
+####################
+# Test fatal syntax errors
+fish: $, is not a valid variable in fish.
+echo $,foo
+      ^
+fish: Unexpected end of string, incomplete parameter expansion
+echo {
+     ^
+
+fish: Unexpected '}' for unopened brace expansion
+echo {}}
+       ^
+

tests/expansion.in

@@ -148,3 +148,9 @@ set testvar "$testvar:FOUR"
 echo "Appended path: $testvar" (count $testvar)
 set --unpath testvar $testvar
 echo "Back to normal variable: $testvar" (count $testvar)
+
+logmsg Test fatal syntax errors
+../test/root/bin/fish -c 'echo $,foo'
+../test/root/bin/fish -c 'echo {'
+../test/root/bin/fish -c 'echo {}}'
+true

tests/expansion.out

@@ -87,3 +87,6 @@ Not a path: ONE:TWO:THREE 1
 As a path: ONE:TWO:THREE 3
 Appended path: ONE:TWO:THREE:FOUR 4
 Back to normal variable: ONE TWO THREE FOUR 4
+
+####################
+# Test fatal syntax errors