patch 9.0.0363: common names in test files causes tests to be flaky

Problem:    Common names in test files causes tests to be flaky.
Solution:   Use more specific names.
diff --git a/src/testdir/test_expand.vim b/src/testdir/test_expand.vim
index cd537f4..8f2fab6 100644
--- a/src/testdir/test_expand.vim
+++ b/src/testdir/test_expand.vim
@@ -57,26 +57,26 @@
   unlet $FOO
 
   new
-  edit Xfile1
-  call assert_equal('e Xfile1', expandcmd('e %'))
-  edit Xfile2
-  edit Xfile1
-  call assert_equal('e Xfile2', 'e #'->expandcmd())
-  edit Xfile2
-  edit Xfile3
-  edit Xfile4
-  let bnum = bufnr('Xfile2')
-  call assert_equal('e Xfile2', expandcmd('e #' . bnum))
+  edit Xpandfile1
+  call assert_equal('e Xpandfile1', expandcmd('e %'))
+  edit Xpandfile2
+  edit Xpandfile1
+  call assert_equal('e Xpandfile2', 'e #'->expandcmd())
+  edit Xpandfile2
+  edit Xpandfile3
+  edit Xpandfile4
+  let bnum = bufnr('Xpandfile2')
+  call assert_equal('e Xpandfile2', expandcmd('e #' . bnum))
   call setline('.', 'Vim!@#')
   call assert_equal('e Vim', expandcmd('e <cword>'))
   call assert_equal('e Vim!@#', expandcmd('e <cWORD>'))
   enew!
-  edit Xfile.java
-  call assert_equal('e Xfile.py', expandcmd('e %:r.py'))
+  edit Xpandfile.java
+  call assert_equal('e Xpandfile.py', expandcmd('e %:r.py'))
   call assert_equal('make abc.java', expandcmd('make abc.%:e'))
-  call assert_equal('make Xabc.java', expandcmd('make %:s?file?abc?'))
+  call assert_equal('make Xabc.java', expandcmd('make %:s?pandfile?abc?'))
   edit a1a2a3.rb
-  call assert_equal('make b1b2b3.rb a1a2a3 Xfile.o', expandcmd('make %:gs?a?b? %< #<.o'))
+  call assert_equal('make b1b2b3.rb a1a2a3 Xpandfile.o', expandcmd('make %:gs?a?b? %< #<.o'))
 
   call assert_equal('make <afile>', expandcmd("make <afile>"))
   call assert_equal('make <amatch>', expandcmd("make <amatch>"))