test: make it possible to test multiple screen string matches

Problem:
Currently it's only possible to test a single string match in the
screen, which makes it hard match multiple strings in the screen to
avoid having to compare the whole screen state.

It's also not possible to test if a string match is not found in the screen.

Solution:
Support an array of `any` matches and also support `none`, which does a
negative comparision.

test/functional/ui/screen.lua

@@ -362,6 +362,7 @@ local expect_keys = {
   condition = true,
   mouse_enabled = true,
   any = true,
+  none = true,
   mode = true,
   unchanged = true,
   intermediate = true,
@@ -408,7 +409,13 @@ end
 --- following chars are magic characters
 ---    ( ) . % + - * ? [ ^ $
 --- and must be escaped with a preceding % for a literal match.
---- @field any? string
+--- @field any? string|table<string>
+---
+--- Lua pattern string expected to not match a screen line. NB: the
+--- following chars are magic characters
+---    ( ) . % + - * ? [ ^ $
+--- and must be escaped with a preceding % for a literal match.
+--- @field none? string|table<string>
 ---
 --- Expected mode as signaled by "mode_change" event
 --- @field mode? string
@@ -492,7 +499,7 @@ function Screen:expect(expected, attr_ids, ...)
     grid = expected.grid
     attr_ids = expected.attr_ids
     condition = expected.condition
-    assert(expected.any == nil or grid == nil)
+    assert((expected.any == nil and expected.none == nil) or grid == nil)
   elseif type(expected) == 'string' then
     grid = expected
     expected = {}
@@ -541,22 +548,55 @@ function Screen:expect(expected, attr_ids, ...)
 
     local actual_rows
     if expected.any or grid then
-      actual_rows = self:render(not expected.any, attr_state)
+      actual_rows = self:render(not (expected.any or expected.none), attr_state)
     end
 
-    if expected.any then
-      -- Search for `any` anywhere in the screen lines.
+    local any_or_none = function(screen_str, value, is_any)
+      if value then
+        local v = value
+        if type(v) == 'string' then
+          v = { v }
+        end
+        local msg
+        if is_any then
+          msg = 'Expected (anywhere): "'
+        else
+          msg = 'Expected (nowhere): "'
+        end
+        for _, v2 in ipairs(v) do
+          local test = screen_str:find(v2)
+          if is_any then
+            test = not test
+          end
+          -- Search for `any` anywhere in the screen lines.
+          if test then
+            return (
+              'Failed to match any screen lines.\n'
+              .. msg
+              .. v2
+              .. '"\n'
+              .. 'Actual:\n  |'
+              .. table.concat(actual_rows, '\n  |')
+              .. '\n\n'
+            )
+          end
+        end
+      end
+      return nil
+    end
+    if expected.any or expected.none then
       local actual_screen_str = table.concat(actual_rows, '\n')
-      if not actual_screen_str:find(expected.any) then
-        return (
-          'Failed to match any screen lines.\n'
-          .. 'Expected (anywhere): "'
-          .. expected.any
-          .. '"\n'
-          .. 'Actual:\n  |'
-          .. table.concat(actual_rows, '\n  |')
-          .. '\n\n'
-        )
+      if expected.any then
+        local res = any_or_none(actual_screen_str, expected.any, true)
+        if res then
+          return res
+        end
+      end
+      if expected.none then
+        local res = any_or_none(actual_screen_str, expected.none, false)
+        if res then
+          return res
+        end
       end
     end