patch 8.0.1153: no tests for diff_hlID() and diff_filler()

Problem:    No tests for diff_hlID() and diff_filler().
Solution:   Add tests. (Dominique Pelle, closes #2156)

src/testdir/test_diffmode.vim

@@ -501,7 +501,7 @@ func Test_diffpatch()
   3
 + 4
 .
-  saveas Xpatch
+  saveas! Xpatch
   bwipe!
   new
   call assert_fails('diffpatch Xpatch', 'E816:')
@@ -547,6 +547,47 @@ func Test_diff_nomodifiable()
   %bwipe!
 endfunc
 
+func Test_diff_hlID()
+  new
+  call setline(1, [1, 2, 3])
+  diffthis
+  vnew
+  call setline(1, ['1x', 2, 'x', 3])
+  diffthis
+  redraw
+
+  call assert_equal(synIDattr(diff_hlID(-1, 1), "name"), "")
+
+  call assert_equal(synIDattr(diff_hlID(1, 1), "name"), "DiffChange")
+  call assert_equal(synIDattr(diff_hlID(1, 2), "name"), "DiffText")
+  call assert_equal(synIDattr(diff_hlID(2, 1), "name"), "")
+  call assert_equal(synIDattr(diff_hlID(3, 1), "name"), "DiffAdd")
+  call assert_equal(synIDattr(diff_hlID(4, 1), "name"), "")
+
+  wincmd w
+  call assert_equal(synIDattr(diff_hlID(1, 1), "name"), "DiffChange")
+  call assert_equal(synIDattr(diff_hlID(2, 1), "name"), "")
+  call assert_equal(synIDattr(diff_hlID(3, 1), "name"), "")
+
+  %bwipe!
+endfunc
+
+func Test_diff_filler()
+  new
+  call setline(1, [1, 2, 3, 'x', 4])
+  diffthis
+  vnew
+  call setline(1, [1, 2, 'y', 'y', 3, 4])
+  diffthis
+  redraw
+
+  call assert_equal([0, 0, 0, 0, 0, 0, 0, 1, 0], map(range(-1, 7), 'diff_filler(v:val)'))
+  wincmd w
+  call assert_equal([0, 0, 0, 0, 2, 0, 0, 0], map(range(-1, 6), 'diff_filler(v:val)'))
+
+  %bwipe!
+endfunc
+
 func Test_diff_lastline()
   enew!
   only!

src/version.c

@@ -761,6 +761,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1153,
 /**/
     1152,
 /**/