patch 9.1.0578: no tests for :Tohtml

Problem:  no tests for :Tohtml
Solution: Add two basic tests (Yinzuo Jiang)

closes: #15240

Signed-off-by: Yinzuo Jiang <jiangyinzuo@foxmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/testdir/Make_all.mak b/src/testdir/Make_all.mak
index 76d4429..71c3dcc 100644
--- a/src/testdir/Make_all.mak
+++ b/src/testdir/Make_all.mak
@@ -315,6 +315,7 @@
 	test_textobjects \
 	test_textprop \
 	test_timers \
+	test_tohtml \
 	test_true_false \
 	test_trycatch \
 	test_undo \
@@ -560,6 +561,7 @@
 	test_textobjects.res \
 	test_textprop.res \
 	test_timers.res \
+	test_tohtml.res \
 	test_true_false.res \
 	test_trycatch.res \
 	test_undo.res \