win: enable job tests that use jobstart only

- echo "" does not hang in powershell
    - cmd.exe's echo command does not hang.
    - job tests default to powershell (WHY?)
- wait 5 seconds for powershell to create an empty file
    - powershell is slow
    - cannot reliably validate the id returned by jobstart via jobpid, jobstop
    - if using cmd.exe, waiting for a second should be enough
- remaining job tests are unreliable in Windows because any build can pass/fail
  for same conditions without changes, especially if the error is in stderr

test/functional/core/job_spec.lua

@@ -60,7 +60,7 @@ describe('jobs', function()
   it('changes to given / directory', function()
     nvim('command', "let g:job_opts.cwd = '/'")
     if iswin() then
-      nvim('command', "let j = jobstart('pwd|%{$_.Path}', g:job_opts)")
+      nvim('command', "let j = jobstart('(Get-Location).Path', g:job_opts)")
     else
       nvim('command', "let j = jobstart('pwd', g:job_opts)")
     end
@@ -75,7 +75,7 @@ describe('jobs', function()
     mkdir(dir)
     nvim('command', "let g:job_opts.cwd = '" .. dir .. "'")
     if iswin() then
-      nvim('command', "let j = jobstart('pwd|%{$_.Path}', g:job_opts)")
+      nvim('command', "let j = jobstart('(Get-Location).Path', g:job_opts)")
     else
       nvim('command', "let j = jobstart('pwd', g:job_opts)")
     end
@@ -115,13 +115,13 @@ describe('jobs', function()
   end)
 
   it('returns -1 when target is not executable #5465', function()
-    if helpers.pending_win32(pending) then return end
     local function new_job()
       return eval([[jobstart('')]])
     end
     local executable_jobid = new_job()
-    local nonexecutable_jobid = eval(
-      "jobstart(['./test/functional/fixtures/non_executable.txt'])")
+    local nonexecutable_jobid = eval("jobstart(['"..(iswin()
+      and './test/functional/fixtures'
+      or  './test/functional/fixtures/non_executable.txt').."'])")
     eq(-1, nonexecutable_jobid)
     -- Should _not_ throw an error.
     eq("", eval("v:errmsg"))
@@ -133,11 +133,10 @@ describe('jobs', function()
     -- TODO: hangs on Windows
     if helpers.pending_win32(pending) then return end
     nvim('command', "let g:job_opts.on_stderr  = function('OnEvent')")
-    nvim('command', "call jobstart('echo', g:job_opts)")
+    nvim('command', [[call jobstart('echo ""', g:job_opts)]])
     expect_twostreams({{'notification', 'stdout', {0, {'', ''}}},
                        {'notification', 'stdout', {0, {''}}}},
                       {{'notification', 'stderr', {0, {''}}}})
-
     eq({'notification', 'exit', {0, 0}}, next_msg())
   end)
 
@@ -253,7 +252,6 @@ describe('jobs', function()
   end)
 
   it('will not leak memory if we leave a job running', function()
-    if helpers.pending_win32(pending) then return end  -- TODO: Need `cat`.
     nvim('command', "call jobstart(['cat', '-'], g:job_opts)")
   end)
 
@@ -300,11 +298,7 @@ describe('jobs', function()
   end)
 
   it('can omit options', function()
-    if helpers.pending_win32(pending) then return end
-    neq(0, nvim('eval', 'delete(".Xtestjob")'))
-    nvim('command', "call jobstart(['touch', '.Xtestjob'])")
-    nvim('command', "sleep 100m")
-    eq(0, nvim('eval', 'delete(".Xtestjob")'))
+    ok(eval([[jobstart('echo ""')]]) > 0)
   end)
 
   it('can omit data callbacks', function()
@@ -348,7 +342,6 @@ describe('jobs', function()
   end)
 
   it('can redefine callbacks being used by a job', function()
-    if helpers.pending_win32(pending) then return end  -- TODO: Need `cat`.
     local screen = Screen.new()
     screen:attach()
     screen:set_default_attr_ids({
@@ -363,7 +356,7 @@ describe('jobs', function()
       \ 'on_stderr': function('g:JobHandler'),
       \ 'on_exit': function('g:JobHandler')
       \ }
-      let job = jobstart('cat -', g:callbacks)
+      let job = jobstart(['cat', '-'], g:callbacks)
     ]])
     wait()
     source([[