vim-patch:8.2.1046: insufficient tests for src/buffer.c (#19903)

Problem:    Insufficient tests for src/buffer.c.
Solution:   Add more tests.  Move comments related tests to a separate file.
            (Yegappan Lakshmanan, closes vim/vim#6325)
b7e2483655

test/functional/legacy/buffer_spec.lua

@@ -0,0 +1,59 @@
+local helpers = require('test.functional.helpers')(after_each)
+local clear, source = helpers.clear, helpers.source
+local call, eq, meths = helpers.call, helpers.eq, helpers.meths
+
+local function expected_empty()
+  eq({}, meths.get_vvar('errors'))
+end
+
+describe('buffer', function()
+  before_each(function()
+    clear()
+    meths.ui_attach(80, 24, {})
+    meths.set_option('hidden', false)
+  end)
+
+  it('deleting a modified buffer with :confirm', function()
+    source([[
+      func Test_bdel_with_confirm()
+        new
+        call setline(1, 'test')
+        call assert_fails('bdel', 'E89:')
+        call nvim_input('c')
+        confirm bdel
+        call assert_equal(2, winnr('$'))
+        call assert_equal(1, &modified)
+        call nvim_input('n')
+        confirm bdel
+        call assert_equal(1, winnr('$'))
+      endfunc
+    ]])
+    call('Test_bdel_with_confirm')
+    expected_empty()
+  end)
+
+  it('editing another buffer from a modified buffer with :confirm', function()
+    source([[
+      func Test_goto_buf_with_confirm()
+        new Xfile
+        enew
+        call setline(1, 'test')
+        call assert_fails('b Xfile', 'E37:')
+        call nvim_input('c')
+        call assert_fails('confirm b Xfile', 'E37:')
+        call assert_equal(1, &modified)
+        call assert_equal('', @%)
+        call nvim_input('y')
+        call assert_fails('confirm b Xfile', 'E37:')
+        call assert_equal(1, &modified)
+        call assert_equal('', @%)
+        call nvim_input('n')
+        confirm b Xfile
+        call assert_equal('Xfile', @%)
+        close!
+      endfunc
+    ]])
+    call('Test_goto_buf_with_confirm')
+    expected_empty()
+  end)
+end)