refactor(tests): merge n.spawn/n.spawn_argv into n.new_session #31859

Problem:
- `n.spawn()` is misleading because it also connects RPC, it's not just
  "spawning" a process.
- It's confusing that `n.spawn()` and `n.spawn_argv()` are separate.

Solution:
- Replace `n.spawn()`/`n.spawn_argv()` with a single function `n.new_session()`.
  This name aligns with the existing functions `n.set_session`/`n.get_session`.
    - Note: removes direct handling of `prepend_argv`, but I doubt that was
      important or intentional. If callers want to control use of `prepend_argv`
      then we should add a new flag to `test.session.Opts`.
- Move `keep` to first parameter of `n.new_session()`.
- Add a `merge` flag to `test.session.Opts`
- Mark `_new_argv()` as private. Test should use clear/new_session/spawn_wait
  instead.

1 files changed, 6 insertions, 7 deletions

diff --git a/test/functional/terminal/tui_spec.lua b/test/functional/terminal/tui_spec.lua
index f9145f9b63..3624a7bc2b 100644
--- a/test/functional/terminal/tui_spec.lua
+++ b/test/functional/terminal/tui_spec.lua
@@ -26,7 +26,6 @@ local api = n.api
 local is_ci = t.is_ci
 local is_os = t.is_os
 local new_pipename = n.new_pipename
-local spawn_argv = n.spawn_argv
 local set_session = n.set_session
 local write_file = t.write_file
 local eval = n.eval
@@ -3320,8 +3319,8 @@ describe('TUI as a client', function()
   end)
 
   it('connects to remote instance (with its own TUI)', function()
-    local server_super = spawn_argv(false) -- equivalent to clear()
-    local client_super = spawn_argv(true)
+    local server_super = n.new_session(false)
+    local client_super = n.new_session(true)
 
     set_session(server_super)
     local server_pipe = new_pipename()
@@ -3395,8 +3394,8 @@ describe('TUI as a client', function()
   end)
 
   it('connects to remote instance (--headless)', function()
-    local server = spawn_argv(false) -- equivalent to clear()
-    local client_super = spawn_argv(true, { env = { NVIM_LOG_FILE = testlog } })
+    local server = n.new_session(false)
+    local client_super = n.new_session(true, { env = { NVIM_LOG_FILE = testlog } })
 
     set_session(server)
     local server_pipe = api.nvim_get_vvar('servername')
@@ -3462,8 +3461,8 @@ describe('TUI as a client', function()
   end)
 
   local function test_remote_tui_quit(status)
-    local server_super = spawn_argv(false) -- equivalent to clear()
-    local client_super = spawn_argv(true)
+    local server_super = n.new_session(false)
+    local client_super = n.new_session(true)
 
     set_session(server_super)
     local server_pipe = new_pipename()