patch 8.0.0440: not enough test coverage in Insert mode

Problem:    Not enough test coverage in Insert mode.
Solution:   Add lots of tests.  Add test_override(). (Christian Brabandt,
            closes #1521)
diff --git a/src/testdir/Make_all.mak b/src/testdir/Make_all.mak
index a0f0036..2642958 100644
--- a/src/testdir/Make_all.mak
+++ b/src/testdir/Make_all.mak
@@ -151,6 +151,7 @@
 	    test_diffmode.res \
 	    test_digraph.res \
 	    test_display.res \
+	    test_edit.res \
 	    test_farsi.res \
 	    test_fnameescape.res \
 	    test_fold.res \