functests: Test invalid behaviour

Test correctly fail for oneline ruby, python and python3.

test/functional/ex_cmds/script_spec.lua

@@ -0,0 +1,75 @@
+local helpers = require('test.functional.helpers')(after_each)
+
+local eq = helpers.eq
+local neq = helpers.neq
+local meths = helpers.meths
+local clear = helpers.clear
+local dedent = helpers.dedent
+local source = helpers.source
+local exc_exec = helpers.exc_exec
+local check_provider = helpers.check_provider
+
+before_each(clear)
+
+describe('script_get-based command', function()
+  local garbage = ')}{+*({}]*[;(+}{&[]}{*])('
+
+  local function test_garbage_exec(cmd, check_neq)
+    describe(cmd, function()
+      it('works correctly when skipping oneline variant', function()
+        eq(true, pcall(source, (dedent([[
+          if 0
+            %s %s
+          endif
+        ]])):format(cmd, garbage)))
+        eq('', meths.command_output('messages'))
+        if check_neq then
+          neq(0, exc_exec(dedent([[
+            %s %s
+          ]])):format(cmd, garbage))
+        end
+      end)
+      it('works correctly when skipping HEREdoc variant', function()
+        eq(true, pcall(source, (dedent([[
+          if 0
+          %s << EOF
+          %s
+          EOF
+          endif
+        ]])):format(cmd, garbage)))
+        eq('', meths.command_output('messages'))
+        if check_neq then
+          eq(true, pcall(source, (dedent([[
+            let g:exc = 0
+            try
+            %s << EOF
+            %s
+            EOF
+            catch
+            let g:exc = v:exception
+            endtry
+          ]])):format(cmd, garbage)))
+          neq(0, meths.get_var('exc'))
+        end
+      end)
+    end)
+  end
+
+  clear()
+
+  -- Built-in scripts
+  test_garbage_exec('lua', true)
+
+  -- Provider-based scripts
+  test_garbage_exec('ruby', check_provider('ruby'))
+  test_garbage_exec('python', check_provider('python'))
+  test_garbage_exec('python3', check_provider('python3'))
+
+  -- Missing scripts
+  test_garbage_exec('tcl', false)
+  test_garbage_exec('mzscheme', false)
+  test_garbage_exec('perl', false)
+
+  -- Not really a script
+  test_garbage_exec('xxxinvalidlanguagexxx', true)
+end)