patch 9.0.1524: passing -1 for bool is not always rejected

Problem:    Passing -1 for bool is not always rejected.
Solution:   Check for error in a better way. (closes #12358)
diff --git a/src/testdir/test_expr.vim b/src/testdir/test_expr.vim
index b3a8c49..68cbeb5 100644
--- a/src/testdir/test_expr.vim
+++ b/src/testdir/test_expr.vim
@@ -161,7 +161,8 @@
   END
   call v9.CheckLegacyAndVim9Success(lines)
 
-  call assert_fails('echo strcharpart("", 0, 0, {})', ['E728:', 'E728:'])
+  call assert_fails('call strcharpart("", 0, 0, {})', ['E728:', 'E728:'])
+  call assert_fails('call strcharpart("", 0, 0, -1)', ['E1023:', 'E1023:'])
 endfunc
 
 func Test_getreg_empty_list()
diff --git a/src/testdir/test_functions.vim b/src/testdir/test_functions.vim
index f05ac15..4529a5e 100644
--- a/src/testdir/test_functions.vim
+++ b/src/testdir/test_functions.vim
@@ -1225,6 +1225,7 @@
   call assert_fails("call byteidx([], 0)", 'E730:')
   call assert_fails("call byteidx('abc', [])", 'E745:')
   call assert_fails("call byteidx('abc', 0, {})", ['E728:', 'E728:'])
+  call assert_fails("call byteidx('abc', 0, -1)", ['E1023:', 'E1023:'])
 endfunc
 
 " Test for byteidxcomp() using a character index
@@ -1265,6 +1266,7 @@
   call assert_fails("call byteidxcomp([], 0)", 'E730:')
   call assert_fails("call byteidxcomp('abc', [])", 'E745:')
   call assert_fails("call byteidxcomp('abc', 0, {})", ['E728:', 'E728:'])
+  call assert_fails("call byteidxcomp('abc', 0, -1)", ['E1023:', 'E1023:'])
 endfunc
 
 " Test for byteidx() using a UTF-16 index
@@ -1625,7 +1627,6 @@
   " error cases
   call assert_equal(-1, utf16idx(test_null_string(), 0, v:true, v:true))
   call assert_fails('let l = utf16idx("ab", 0, v:false, [])', 'E1212:')
-  call assert_fails('echo strchars("", {})', ['E728:', 'E728:'])
 endfunc
 
 " Test for strutf16len()
diff --git a/src/testdir/test_utf8.vim b/src/testdir/test_utf8.vim
index 16bf60d..610566f 100644
--- a/src/testdir/test_utf8.vim
+++ b/src/testdir/test_utf8.vim
@@ -29,8 +29,10 @@
     call assert_equal(exp[i], strcharlen(inp[i]))
   endfor
 
-  call assert_fails("let v=strchars('abc', [])", 'E745:')
-  call assert_fails("let v=strchars('abc', 2)", 'E1023:')
+  call assert_fails("call strchars('abc', 2)", ['E1023:', 'E1023:'])
+  call assert_fails("call strchars('abc', -1)", ['E1023:', 'E1023:'])
+  call assert_fails("call strchars('abc', {})", ['E728:', 'E728:'])
+  call assert_fails("call strchars('abc', [])", ['E745:', 'E745:'])
 endfunc
 
 " Test for customlist completion