diff --git a/src/testdir/test_blob.vim b/src/testdir/test_blob.vim
index 4b6774f..3c15101 100644
--- a/src/testdir/test_blob.vim
+++ b/src/testdir/test_blob.vim
@@ -142,6 +142,7 @@
   let b2 = b1[:]
   call assert_true(b1 == b2)
   call assert_false(b1 is b2)
+  call assert_true(b1 isnot b2)
 
   call assert_fails('let x = b1 > b2')
   call assert_fails('let x = b1 < b2')
diff --git a/src/testdir/test_channel.vim b/src/testdir/test_channel.vim
index cf51a53..9c51c64 100644
--- a/src/testdir/test_channel.vim
+++ b/src/testdir/test_channel.vim
@@ -1203,6 +1203,7 @@
 	\  'err_cb': dict.errHandler,
 	\  'err_mode': 'json'})
   call assert_equal("run", job_status(job))
+  call test_garbagecollect_now()
   try
     let g:Ch_outmsg = ''
     let g:Ch_errmsg = ''
@@ -1818,6 +1819,7 @@
   let g:out = ''
   let arg = 'import sys;sys.stdout.write("1\n2\n3")'
   call job_start([s:python, '-c', arg], {'close_cb': function('s:close_cb')})
+  call test_garbagecollect_now()
   call WaitForAssert({-> assert_equal('123', g:out)})
   unlet g:out
   delfunc s:close_cb
@@ -1828,6 +1830,7 @@
   let arg = 'import os,sys;os.close(1);sys.stderr.write("test\n")'
   call job_start([s:python, '-c', arg], {'callback': {-> execute('let g:linecount += 1')}})
   call WaitForAssert({-> assert_equal(1, g:linecount)})
+  call test_garbagecollect_now()
   unlet g:linecount
 endfunc
 
diff --git a/src/testdir/test_eval_stuff.vim b/src/testdir/test_eval_stuff.vim
index 8feeb36..cd9611c 100644
--- a/src/testdir/test_eval_stuff.vim
+++ b/src/testdir/test_eval_stuff.vim
@@ -217,7 +217,7 @@
   call delete('Xversionscript')
 endfunc
 
-func Test_excute_null()
+func Test_execute_cmd_with_null()
   call assert_fails('execute test_null_list()', 'E730:')
   call assert_fails('execute test_null_dict()', 'E731:')
   call assert_fails('execute test_null_blob()', 'E976:')
diff --git a/src/testdir/test_execute_func.vim b/src/testdir/test_execute_func.vim
index 235107c..e02b08e 100644
--- a/src/testdir/test_execute_func.vim
+++ b/src/testdir/test_execute_func.vim
@@ -132,7 +132,7 @@
   unlet xyz
 endfunc
 
-func Test_execute_null()
+func Test_execute_func_with_null()
   call assert_equal("", execute(test_null_string()))
   call assert_equal("", execute(test_null_list()))
   call assert_fails('call execute(test_null_dict())', 'E731:')
@@ -143,3 +143,5 @@
     call assert_fails('call execute(test_null_channel())', 'E908:')
   endif
 endfunc
+
+" vim: shiftwidth=2 sts=2 expandtab
diff --git a/src/testdir/test_expr.vim b/src/testdir/test_expr.vim
index ce16793..c8b5464 100644
--- a/src/testdir/test_expr.vim
+++ b/src/testdir/test_expr.vim
@@ -1,5 +1,7 @@
 " Tests for expressions.
 
+source check.vim
+
 func Test_equal()
   let base = {}
   func base.method()
@@ -20,6 +22,8 @@
   call assert_false([base.method] == [instance.other])
 
   call assert_fails('echo base.method > instance.method')
+  call assert_equal(0, test_null_function() == function('min'))
+  call assert_equal(1, test_null_function() == test_null_function())
 endfunc
 
 func Test_version()
@@ -583,4 +587,24 @@
   call assert_fails("let v = -{}", 'E728:')
 endfunc
 
+" Test for float value comparison
+func Test_float_compare()
+  CheckFeature float
+  call assert_true(1.2 == 1.2)
+  call assert_true(1.0 != 1.2)
+  call assert_true(1.2 > 1.0)
+  call assert_true(1.2 >= 1.2)
+  call assert_true(1.0 < 1.2)
+  call assert_true(1.2 <= 1.2)
+  call assert_true(+0.0 == -0.0)
+  " two NaNs (not a number) are not equal
+  call assert_true(sqrt(-4.01) != (0.0 / 0.0))
+  " two inf (infinity) are equal
+  call assert_true((1.0 / 0) == (2.0 / 0))
+  " two -inf (infinity) are equal
+  call assert_true(-(1.0 / 0) == -(2.0 / 0))
+  " +infinity != -infinity
+  call assert_true((1.0 / 0) != -(2.0 / 0))
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab
diff --git a/src/testdir/test_filter_map.vim b/src/testdir/test_filter_map.vim
index fc9c741..0e47bad 100644
--- a/src/testdir/test_filter_map.vim
+++ b/src/testdir/test_filter_map.vim
@@ -99,6 +99,10 @@
   call assert_fails("let l = filter([1, 2], {})", 'E731:')
   call assert_equal(0, map(test_null_list(), '"> " .. v:val'))
   call assert_equal(0, map(test_null_dict(), '"> " .. v:val'))
+  call assert_equal([1, 2, 3], filter([1, 2, 3], test_null_function()))
+  call assert_fails("let l = filter([1, 2], function('min'))", 'E118:')
+  call assert_equal([1, 2, 3], filter([1, 2, 3], test_null_partial()))
+  call assert_fails("let l = filter([1, 2], {a, b, c -> 1})", 'E119:')
 endfunc
 
 func Test_map_and_modify()
diff --git a/src/testdir/test_fold.vim b/src/testdir/test_fold.vim
index 36de136..5a4632a 100644
--- a/src/testdir/test_fold.vim
+++ b/src/testdir/test_fold.vim
@@ -794,3 +794,28 @@
   bwipe!
   set foldmethod&
 endfunc
+
+" Test for errors in 'foldexpr'
+func Test_fold_expr_error()
+  new
+  call setline(1, ['one', 'two', 'three'])
+
+  " Return a list from the expression
+  set foldexpr=[]
+  set foldmethod=expr
+  for i in range(3)
+    call assert_equal(0, foldlevel(i))
+  endfor
+
+  " expression error
+  set foldexpr=[{]
+  set foldmethod=expr
+  for i in range(3)
+    call assert_equal(0, foldlevel(i))
+  endfor
+
+  set foldmethod& foldexpr&
+  close!
+endfunc
+
+" vim: shiftwidth=2 sts=2 expandtab
diff --git a/src/testdir/test_functions.vim b/src/testdir/test_functions.vim
index dbd0804..029ea5b 100644
--- a/src/testdir/test_functions.vim
+++ b/src/testdir/test_functions.vim
@@ -1239,6 +1239,8 @@
   call assert_equal(0, col([2, '$']))
   call assert_equal(0, col([1, 100]))
   call assert_equal(0, col([1]))
+  call assert_equal(0, col(test_null_list()))
+  call assert_fails('let c = col({})', 'E731:')
 
   " test for getting the visual start column
   func T()
diff --git a/src/testdir/test_let.vim b/src/testdir/test_let.vim
index e0d543c..f135a2f 100644
--- a/src/testdir/test_let.vim
+++ b/src/testdir/test_let.vim
@@ -81,6 +81,24 @@
   let l:Test_Local_Var = {'k' : 5}
   call assert_match("\nl:Test_Local_Var      {'k': 5}", execute('let l:'))
   call assert_match("v:errors              []", execute('let v:'))
+
+  " Test for assigning multiple list items
+  let l = [1, 2, 3]
+  let [l[0], l[1]] = [10, 20]
+  call assert_equal([10, 20, 3], l)
+
+  " Test for errors in conditional expression
+  call assert_fails('let val = [] ? 1 : 2', 'E745:')
+  call assert_fails('let val = 1 ? 5+ : 6', 'E121:')
+  call assert_fails('let val = 1 ? 0 : 5+', 'E15:')
+  call assert_false(exists('val'))
+
+  " Test for errors in logical operators
+  let @a = 'if [] || 0 | let val = 2 | endif'
+  call assert_fails('exe @a', 'E745:')
+  call assert_fails('call feedkeys(":let val = 0 || []\<cr>", "xt")', 'E745:')
+  call assert_fails('exe "let val = [] && 5"', 'E745:')
+  call assert_fails('exe "let val = 6 && []"', 'E745:')
 endfunc
 
 func s:set_arg1(a) abort
@@ -282,13 +300,20 @@
   let d = {'k' : 4}
   call assert_fails('let d.# = 5', 'E713:')
   call assert_fails('let d.m += 5', 'E734:')
+  call assert_fails('let m = d[{]', 'E15:')
   let l = [1, 2]
   call assert_fails('let l[2] = 0', 'E684:')
   call assert_fails('let l[0:1] = [1, 2, 3]', 'E710:')
   call assert_fails('let l[-2:-3] = [3, 4]', 'E684:')
   call assert_fails('let l[0:4] = [5, 6]', 'E711:')
+  call assert_fails('let l -= 2', 'E734:')
+  call assert_fails('let l += 2', 'E734:')
   call assert_fails('let g:["a;b"] = 10', 'E461:')
   call assert_fails('let g:.min = function("max")', 'E704:')
+  if has('channel')
+    let ch = test_null_channel()
+    call assert_fails('let ch += 1', 'E734:')
+  endif
 
   " This test works only when the language is English
   if v:lang == "C" || v:lang =~ '^[Ee]n'
diff --git a/src/testdir/test_listdict.vim b/src/testdir/test_listdict.vim
index a2cc6b5..87d7a2c 100644
--- a/src/testdir/test_listdict.vim
+++ b/src/testdir/test_listdict.vim
@@ -943,6 +943,7 @@
   call assert_equal(0, uniq(l))
   call assert_fails("let k = [] + l", 'E15:')
   call assert_fails("let k = l + []", 'E15:')
+  call assert_equal(0, len(copy(test_null_list())))
 endfunc
 
 " Test for a null dict
@@ -959,6 +960,7 @@
   call assert_equal('{}', string(d))
   call assert_fails('let x = test_null_dict()[10]')
   call assert_equal({}, {})
+  call assert_equal(0, len(copy(test_null_dict())))
 endfunc
 
 " vim: shiftwidth=2 sts=2 expandtab
diff --git a/src/testdir/test_partial.vim b/src/testdir/test_partial.vim
index 1e682d5..5b273db 100644
--- a/src/testdir/test_partial.vim
+++ b/src/testdir/test_partial.vim
@@ -63,6 +63,7 @@
 func Test_partial_dict()
   let dict = {'name': 'hello'}
   let Cb = function('MyDictFunc', ["foo", "bar"], dict)
+  call test_garbagecollect_now()
   call assert_equal("hello/foo/bar", Cb())
   call assert_fails('Cb("xxx")', 'E492:')
 
@@ -282,6 +283,7 @@
     let g:ref_job = job_start('echo')
     let d = {'a': 'b'}
     call job_setoptions(g:ref_job, {'exit_cb': function('Ignored2', [], d)})
+    call test_garbagecollect_now()
   endif
 endfunc
 
@@ -391,6 +393,16 @@
   call assert_true(F1 isnot# F2)  " Different functions
   call assert_true(F1 isnot# F1d1)  " Partial /= non-partial
   call assert_true(d1.f1 isnot# d1.f1)  " handle_subscript creates new partial each time
+
+  " compare two null partials
+  let N1 = test_null_partial()
+  let N2 = N1
+  call assert_true(N1 is N2)
+  call assert_true(N1 == N2)
+
+  " compare a partial and a null partial
+  call assert_false(N1 == F1)
+  call assert_false(F1 is N1)
 endfunc
 
 " vim: shiftwidth=2 sts=2 expandtab
diff --git a/src/testdir/test_usercommands.vim b/src/testdir/test_usercommands.vim
index 7f87e27..c38424f 100644
--- a/src/testdir/test_usercommands.vim
+++ b/src/testdir/test_usercommands.vim
@@ -364,6 +364,10 @@
   com! -complete=custom, DoCmd
   call assert_beeps("call feedkeys(':DoCmd \t', 'tx')")
 
+  " custom completion failure with the wrong function
+  com! -complete=custom,min DoCmd
+  call assert_fails("call feedkeys(':DoCmd \t', 'tx')", 'E118:')
+
   delcom DoCmd
 endfunc