diff --git a/src/misc1.c b/src/misc1.c
index b391cb1ee4..e78343291b 100644
--- a/src/misc1.c
+++ b/src/misc1.c
@@ -3256,34 +3256,17 @@ char_u *get_env_name(expand_T *xp, int idx)
  * Find all user names for user completion.
  * Done only once and then cached.
  */
-static void init_users(void)                 {
+static void init_users(void)
+{
   static int lazy_init_done = FALSE;
 
-  if (lazy_init_done)
+  if (lazy_init_done) {
     return;
+  }
 
   lazy_init_done = TRUE;
-  ga_init2(&ga_users, sizeof(char_u *), 20);
-
-# if defined(HAVE_GETPWENT) && defined(HAVE_PWD_H)
-  {
-    char_u*         user;
-    struct passwd*  pw;
-
-    setpwent();
-    while ((pw = getpwent()) != NULL)
-      /* pw->pw_name shouldn't be NULL but just in case... */
-      if (pw->pw_name != NULL) {
-        if (ga_grow(&ga_users, 1) == FAIL)
-          break;
-        user = vim_strsave((char_u*)pw->pw_name);
-        if (user == NULL)
-          break;
-        ((char_u **)(ga_users.ga_data))[ga_users.ga_len++] = user;
-      }
-    endpwent();
-  }
-# endif
+  
+  mch_get_usernames(&ga_users);
 }
 
 /*
diff --git a/src/os/os.h b/src/os/os.h
index 48e3ffd0dd..87323fb025 100644
--- a/src/os/os.h
+++ b/src/os/os.h
@@ -13,5 +13,6 @@ int mch_can_exe(const char_u *name);
 const char *mch_getenv(const char *name);
 int mch_setenv(const char *name, const char *value, int overwrite);
 char *mch_getenvname_at_index(size_t index);
+int mch_get_usernames(garray_T *usernames);
 
 #endif
diff --git a/src/os/users.c b/src/os/users.c
new file mode 100644
index 0000000000..b392118f1b
--- /dev/null
+++ b/src/os/users.c
@@ -0,0 +1,57 @@
+/* vi:set ts=2 sts=2 sw=2:
+ *
+ * VIM - Vi IMproved	by Bram Moolenaar
+ *
+ * Do ":help uganda"  in Vim to read copying and usage conditions.
+ * Do ":help credits" in Vim to see a list of people who contributed.
+ * See README.txt for an overview of the Vim source code.
+ */
+
+/*
+ * users.c -- operating system user information
+ */
+
+#include <uv.h>
+
+#include "os.h"
+#include "../garray.h"
+#include "../misc2.h"
+#ifdef HAVE_PWD_H
+# include <pwd.h>
+#endif
+
+/*
+ * Initialize users garray and fill it with os usernames.
+ * Return Ok for success, FAIL for failure.
+ */
+int mch_get_usernames(garray_T *users)
+{
+  if (users == NULL) {
+    return FALSE;
+  }
+  ga_init2(users, sizeof(char *), 20);
+
+# if defined(HAVE_GETPWENT) && defined(HAVE_PWD_H)
+  char *user;
+  struct passwd *pw;
+
+  setpwent();
+  while ((pw = getpwent()) != NULL) {
+    /* pw->pw_name shouldn't be NULL but just in case... */
+    if (pw->pw_name != NULL) {
+      if (ga_grow(users, 1) == FAIL) {
+        return FAIL;
+      }
+      user = (char *)vim_strsave((char_u*)pw->pw_name);
+      if (user == NULL) {
+        return FAIL;
+      }
+      ((char **)(users->ga_data))[users->ga_len++] = user;
+    }
+  }
+  endpwent();
+# endif
+
+  return OK;
+}
+
diff --git a/test/unit/os/users.moon b/test/unit/os/users.moon
new file mode 100644
index 0000000000..366407d5c8
--- /dev/null
+++ b/test/unit/os/users.moon
@@ -0,0 +1,52 @@
+{:cimport, :internalize, :eq, :ffi, :lib, :cstr} = require 'test.unit.helpers'
+
+-- fs = cimport './src/os/os.h'
+-- remove these statements once 'cimport' is working properly for misc1.h
+users = lib
+ffi.cdef [[
+typedef struct growarray {
+  int ga_len;
+  int ga_maxlen;
+  int ga_itemsize;
+  int ga_growsize;
+  void    *ga_data;
+} garray_T;
+int mch_get_usernames(garray_T *usernames);
+]]
+
+NULL = ffi.cast 'void*', 0
+OK = 1
+FAIL = 0
+
+garray_new = () ->
+  ffi.new 'garray_T[1]'
+
+garray_get_len = (array) ->
+  array[0].ga_len
+
+garray_get_item = (array, index) ->
+  (ffi.cast 'void **', array[0].ga_data)[index]
+
+
+describe 'users function', ->
+
+  describe 'mch_get_usernames', ->
+
+    -- will probably not work on windows
+    current_username = os.getenv 'USER'
+
+    it 'returns FAIL if called with NULL', ->
+      eq FAIL, users.mch_get_usernames NULL
+
+    it 'fills the names garray with os usernames and returns OK', ->
+      ga_users = garray_new!
+      eq OK, users.mch_get_usernames ga_users
+      user_count = garray_get_len ga_users
+      assert.is_true user_count > 0
+      current_username_found = false
+      for i = 0, user_count - 1
+        name = ffi.string (garray_get_item ga_users, i)
+        if name == current_username
+          current_username_found = true
+      assert.is_true current_username_found
+