patch 8.2.4407: Vim9: some code not covered by tests

Problem:    Vim9: some code not covered by tests.
Solution:   Add more tests.  Avoid giving two errors.  Remove dead code.

src/testdir/test_vim9_assign.vim

@@ -543,6 +543,13 @@ def Test_assign_index()
   d3.one.two.three = 123
   assert_equal({one: {two: {three: 123}}}, d3)
 
+  # blob
+  var bl: blob = 0z11223344
+  bl[0] = 0x77
+  assert_equal(0z77223344, bl)
+  bl[-2] = 0x66
+  assert_equal(0z77226644, bl)
+
   # should not read the next line when generating "a.b"
   var a = {}
   a.b = {}
@@ -591,6 +598,18 @@ def Test_assign_index()
       dl.one = {}
   END
   v9.CheckDefFailure(lines, 'E1012: Type mismatch; expected list<number> but got dict<unknown>', 2)
+
+  lines =<< trim END
+      g:l = [1, 2]
+      g:l['x'] = 3
+  END
+  v9.CheckDefExecAndScriptFailure(lines, ['E39:', 'E1030:'], 2)
+
+  lines =<< trim END
+    var bl: blob = test_null_blob()
+    bl[1] = 8
+  END
+  v9.CheckDefExecAndScriptFailure(lines, ['E1184:', 'E979:'], 2)
 enddef
 
 def Test_init_in_for_loop()
@@ -1201,6 +1220,21 @@ def Test_assignment_default()
   assert_equal(5678, nr)
 enddef
 
+def Test_script_var_default()
+  var lines =<< trim END
+      vim9script
+      var l: list<number>
+      var bl: blob
+      var d: dict<number>
+      def Echo()
+        assert_equal([], l)
+        assert_equal(0z, bl)
+        assert_equal({}, d)
+      enddef
+  END
+  v9.CheckScriptSuccess(lines)
+enddef
+
 let s:scriptvar = 'init'
 
 def Test_assignment_var_list()
@@ -2082,6 +2116,25 @@ def Test_unlet()
     'var ll = [1, 2]',
     'unlet ll[0: 1]',
     ], 'E1004:', 2)
+
+  v9.CheckDefExecFailure([
+    'g:ll = [1, 2]',
+    'g:idx = "x"',
+    'unlet g:ll[g:idx]',
+    ], 'E1029: Expected number but got string', 3)
+
+  v9.CheckDefExecFailure([
+    'g:ll = [1, 2, 3]',
+    'g:idx = "x"',
+    'unlet g:ll[g:idx : 2]',
+    ], 'E1029: Expected number but got string', 3)
+
+  v9.CheckDefExecFailure([
+    'g:ll = [1, 2, 3]',
+    'g:idx = "x"',
+    'unlet g:ll[0 : g:idx]',
+    ], 'E1029: Expected number but got string', 3)
+
   # command recognized as assignment when skipping, should not give an error
   v9.CheckScriptSuccess([
     'vim9script',