patch 8.1.1048: minor issues with tests

Problem:    Minor issues with tests.
Solution:   Delete unused test OK file.  Add missing entries in list of tests.
            Fix readme file. (Masato Nishihata, closes #4160)
diff --git a/src/testdir/README.txt b/src/testdir/README.txt
index f4486e3..76396fe 100644
--- a/src/testdir/README.txt
+++ b/src/testdir/README.txt
@@ -34,17 +34,14 @@
 
 - Use try/catch to avoid an exception aborts the test.
 
-- Use alloc_fail() to have memory allocation fail. This makes it possible to
-  check memory allocation failures are handled gracefully.  You need to change
-
-- the source code to add an ID to the allocation.  Update LAST_ID_USED above
-  alloc_id() to the highest ID used.
+- Use test_alloc_fail() to have memory allocation fail.  This makes it possible
+  to check memory allocation failures are handled gracefully.  You need to
+  change the source code to add an ID to the allocation.  Add a new one to
+  alloc_id_T, before aid_last.
 
 - Use test_override() to make Vim behave differently, e.g.  if char_avail()
   must return FALSE for a while.  E.g. to trigger the CursorMovedI autocommand
-  event.
-
-- See test_cursor_func.vim for an example.
+  event. See test_cursor_func.vim for an example.
 
 - If the bug that is being tested isn't fixed yet, you can throw an exception
   with "Skipped" so that it's clear this still needs work.  E.g.: throw
@@ -64,7 +61,7 @@
 1) Create test_<subject>.in and test_<subject>.ok files.
 2) Add test_<subject>.out to SCRIPTS_ALL in Make_all.mak in alphabetical order.
 3) Use make test_<subject>.out to run a single test in src/testdir/.
-   Use make test_<subject>  to run a single test in src/.
+   Use make test_<subject> to run a single test in src/.
 4) Also add an entry in src/Makefile.
 
 Keep in mind that the files are used as if everything was typed: