unittests: Do not import libnvim or headers in main process

Slows down unit tests much, but gets rid of as much preserved state as possible.

test/unit/os/fs_spec.lua

@@ -16,10 +16,10 @@ local to_cstr = helpers.to_cstr
 local OK = helpers.OK
 local FAIL = helpers.FAIL
 local NULL = helpers.NULL
+
 local NODE_NORMAL = 0
 local NODE_WRITABLE = 1
 
-cimport('unistd.h')
 cimport('./src/nvim/os/shell.h')
 cimport('./src/nvim/option_defs.h')
 cimport('./src/nvim/main.h')
@@ -66,13 +66,10 @@ local function os_getperm(filename)
 end
 
 describe('fs function', function()
-  local orig_test_file_perm
-
-  setup(function()
+  before_each(function()
     lfs.mkdir('unit-test-directory');
 
     io.open('unit-test-directory/test.file', 'w').close()
-    orig_test_file_perm = os_getperm('unit-test-directory/test.file')
 
     io.open('unit-test-directory/test_2.file', 'w').close()
     lfs.link('test.file', 'unit-test-directory/test_link.file', true)
@@ -84,7 +81,7 @@ describe('fs function', function()
     directory, executable_name = string.match(absolute_executable, '^(.*)/(.*)$')
   end)
 
-  teardown(function()
+  after_each(function()
     os.remove('unit-test-directory/test.file')
     os.remove('unit-test-directory/test_2.file')
     os.remove('unit-test-directory/test_link.file')
@@ -217,10 +214,6 @@ describe('fs function', function()
   end)
 
   describe('file permissions', function()
-    before_each(function()
-      os_setperm('unit-test-directory/test.file', orig_test_file_perm)
-    end)
-
     local function os_fchown(filename, user_id, group_id)
       local fd = ffi.C.open(filename, 0)
       local res = fs.os_fchown(fd, user_id, group_id)

test/unit/os/shell_spec.lua

@@ -11,6 +11,7 @@ local ffi, eq = helpers.ffi, helpers.eq
 local intern = helpers.internalize
 local to_cstr = helpers.to_cstr
 local NULL = ffi.cast('void *', 0)
+local deferred_call = deferred_call
 
 describe('shell functions', function()
   before_each(function()
@@ -73,25 +74,13 @@ describe('shell functions', function()
       eq(0, status)
     end)
 
-    it ('returns non-zero exit code', function()
+    itp('returns non-zero exit code', function()
       local status = os_system('exit 2')
       eq(2, status)
     end)
   end)
 
   describe('shell_build_argv', function()
-    local saved_opts = {}
-
-    setup(function()
-      saved_opts.p_sh = cimported.p_sh
-      saved_opts.p_shcf = cimported.p_shcf
-    end)
-
-    teardown(function()
-      cimported.p_sh = saved_opts.p_sh
-      cimported.p_shcf = saved_opts.p_shcf
-    end)
-
     itp('works with NULL arguments', function()
       eq({'/bin/bash'}, shell_build_argv(nil, nil))
     end)