test: start test runners in Xtest_xdg dir (#37964)

This is a better way to prevent parallel tests from interfering with
each other, as there are many ways files can be created and deleted in
tests, so enforcing different file names is hard.

Using $TMPDIR can also work in most cases, but 'backipskip' etc. have
special defaults for $TMPDIR.

Symlink runtime/, src/, test/ and README.md to Xtest_xdg dir to make
tests more convenient (and symlinking test/ is required for busted).

Also, use README.md instead of test/README.md in the Ex mode inccommand
test, as test/README.md no longer contains 'N' char.

3 files changed, 15 insertions, 1 deletions

diff --git a/test/functional/vimscript/executable_spec.lua b/test/functional/vimscript/executable_spec.lua
index 05d249ca32..3840f55e84 100644
--- a/test/functional/vimscript/executable_spec.lua
+++ b/test/functional/vimscript/executable_spec.lua
@@ -20,6 +20,9 @@ describe('executable()', function()
 
   if is_os('win') then
     it('exepath respects shellslash', function()
+      -- test/ cannot be a symlink in this test.
+      n.api.nvim_set_current_dir(t.paths.test_source_path)
+
       command('let $PATH = fnamemodify("./test/functional/fixtures/bin", ":p")')
       eq(
         [[test\functional\fixtures\bin\null.CMD]],
@@ -33,6 +36,9 @@ describe('executable()', function()
     end)
 
     it('stdpath respects shellslash', function()
+      -- Needs to check paths relative to repo root dir.
+      n.api.nvim_set_current_dir(t.paths.test_source_path)
+
       t.matches(
         [[build\Xtest_xdg[%w_]*\share\nvim%-data]],
         call('fnamemodify', call('stdpath', 'data'), ':.')
diff --git a/test/functional/vimscript/fnamemodify_spec.lua b/test/functional/vimscript/fnamemodify_spec.lua
index f2cee9b83e..8b0b242c62 100644
--- a/test/functional/vimscript/fnamemodify_spec.lua
+++ b/test/functional/vimscript/fnamemodify_spec.lua
@@ -45,6 +45,9 @@ describe('fnamemodify()', function()
   end)
 
   it('handles examples from ":help filename-modifiers"', function()
+    -- src/ cannot be a symlink in this test.
+    n.api.nvim_set_current_dir(t.paths.test_source_path)
+
     local filename = 'src/version.c'
     local cwd = getcwd()
 
diff --git a/test/functional/vimscript/system_spec.lua b/test/functional/vimscript/system_spec.lua
index 54650caa71..67a613d848 100644
--- a/test/functional/vimscript/system_spec.lua
+++ b/test/functional/vimscript/system_spec.lua
@@ -131,11 +131,16 @@ describe('system()', function()
 
     before_each(function()
       screen = Screen.new()
+      t.write_file('Xmorefile', ('line1\nline2\nline3\n'):rep(10))
+    end)
+
+    after_each(function()
+      os.remove('Xmorefile')
     end)
 
     if is_os('win') then
       local function test_more()
-        eq('root = true', eval([[get(split(system('"more" ".editorconfig"'), "\n"), 0, '')]]))
+        eq('line1', eval([[get(split(system('"more" "Xmorefile"'), "\n"), 0, '')]]))
       end
       local function test_shell_unquoting()
         eval([[system('"ping" "-n" "1" "127.0.0.1"')]])