diff --git a/src/nvim/testdir/Makefile b/src/nvim/testdir/Makefile
index efcb8a68d2..381d1727da 100644
--- a/src/nvim/testdir/Makefile
+++ b/src/nvim/testdir/Makefile
@@ -31,8 +31,7 @@ SCRIPTS := test_eval.out                                               \
            test_command_count.out                                      \
            test_cdo.out                                                \
 
-NEW_TESTS = test_assert.res \
-	    test_undolevels.res
+NEW_TESTS = test_undolevels.res
 
 SCRIPTS_GUI := test16.out
 
diff --git a/src/nvim/testdir/test_assert.vim b/src/nvim/testdir/test_assert.vim
deleted file mode 100644
index 049ce98859..0000000000
--- a/src/nvim/testdir/test_assert.vim
+++ /dev/null
@@ -1,19 +0,0 @@
-" Test that the methods used for testing work.
-
-func Test_assert_false()
-  call assert_false(0)
-endfunc
-
-func Test_assert_true()
-  call assert_true(1)
-  call assert_true(123)
-endfunc
-
-func Test_assert_equal()
-  let s = 'foo'
-  call assert_equal('foo', s)
-  let n = 4
-  call assert_equal(4, n)
-  let l = [1, 2, 3]
-  call assert_equal([1, 2, 3], l)
-endfunc
diff --git a/test/functional/legacy/assert_spec.lua b/test/functional/legacy/assert_spec.lua
new file mode 100644
index 0000000000..5d91aa9099
--- /dev/null
+++ b/test/functional/legacy/assert_spec.lua
@@ -0,0 +1,153 @@
+local helpers = require('test.functional.helpers')
+local nvim, call = helpers.meths, helpers.call
+local clear, eq = helpers.clear, helpers.eq
+local write_file, execute = helpers.write_file, helpers.execute
+
+local function expected_errors(errors)
+  eq(errors, nvim.get_vvar('errors'))
+end
+
+local function expected_empty()
+  eq({}, nvim.get_vvar('errors'))
+end
+
+local function source(code)
+  local tmpname = os.tmpname()
+  write_file(tmpname, code)
+  nvim.command('source '..tmpname)
+  os.remove(tmpname)
+  return tmpname
+end
+
+describe('assert function:', function()
+
+  before_each(function()
+    clear()
+  end)
+
+  -- assert_equal({expected}, {actual}, [, {msg}])
+  describe('assert_equal', function()
+    it('should not change v:errors when expected is equal to actual', function()
+      source([[
+        let s = 'foo'
+        call assert_equal('foo', s)
+        let n = 4
+        call assert_equal(4, n)
+        let l = [1, 2, 3]
+        call assert_equal([1, 2, 3], l)
+        fu Func()
+        endfu
+        let F1 = function('Func')
+        let F2 = function('Func')
+        call assert_equal(F1, F2)
+      ]])
+      expected_empty()
+    end)
+
+    it('should not change v:errors when expected is equal to actual', function()
+      call('assert_equal', '', '')
+      call('assert_equal', 'string', 'string')
+      expected_empty()
+    end)
+
+    it('should change v:errors when expected is not equal to actual', function()
+      call('assert_equal', 0, {0})
+      expected_errors({'Expected 0 but got [0]'})
+    end)
+
+    it('should change v:errors when expected is not equal to actual', function()
+      call('assert_equal', 0, "0")
+      expected_errors({"Expected 0 but got '0'"})
+    end)
+
+    it('should change v:errors when expected is not equal to actual', function()
+      -- Lua does not tell integer from float.
+      execute('call assert_equal(1, 1.0)')
+      expected_errors({'Expected 1 but got 1.0'})
+    end)
+
+    it('should change v:errors when expected is not equal to actual', function()
+      call('assert_equal', 'true', 'false')
+      expected_errors({"Expected 'true' but got 'false'"})
+    end)
+  end)
+
+  -- assert_false({actual}, [, {msg}])
+  describe('assert_false', function()
+    it('should not change v:errors when actual is false', function()
+      call('assert_false', 0)
+      call('assert_false', false)
+      expected_empty()
+    end)
+
+    it('should change v:errors when actual is not false', function()
+      call('assert_false', 1)
+      expected_errors({'Expected False but got 1'})
+    end)
+
+    it('should change v:errors when actual is not false', function()
+      call('assert_false', {})
+      expected_errors({'Expected False but got []'})
+    end)
+  end)
+
+  -- assert_true({actual}, [, {msg}])
+  describe('assert_true', function()
+    it('should not change v:errors when actual is true', function()
+      call('assert_true', 1)
+      call('assert_true', -1) -- In Vim script, non-zero Numbers are TRUE.
+      call('assert_true', true)
+      expected_empty()
+    end)
+
+    it('should change v:errors when actual is not true', function()
+      call('assert_true', 1.5)
+      expected_errors({'Expected True but got 1.5'})
+    end)
+  end)
+
+  describe('v:errors', function()
+    it('should be initialized at startup', function()
+      expected_empty()
+    end)
+
+    it('should have function names and relative line numbers', function()
+      source([[
+        fu Func_one()
+          call assert_equal([0], {'0' : 0})
+          call assert_false('False')
+          call assert_true("True")
+        endfu
+        fu Func_two()
+          " for shifting a line number
+          call assert_true('line two')
+        endfu
+      ]])
+      call('Func_one')
+      call('Func_two')
+      expected_errors({
+        "function Func_one line 1: Expected [0] but got {'0': 0}",
+        "function Func_one line 2: Expected False but got 'False'",
+        "function Func_one line 3: Expected True but got 'True'",
+        "function Func_two line 2: Expected True but got 'line two'",
+      })
+    end)
+
+    it('should have file names and passed messages', function()
+      local tmpname_one = source([[
+        call assert_equal(1, 100, 'equal assertion failed')
+        call assert_false('true', 'true  assertion failed')
+        call assert_true('false', 'false assertion failed')
+      ]])
+      local tmpname_two = source([[
+        call assert_true('', 'file two')
+      ]])
+      expected_errors({
+        tmpname_one .. " line 1: 'equal assertion failed'",
+        tmpname_one .. " line 2: 'true  assertion failed'",
+        tmpname_one .. " line 3: 'false assertion failed'",
+        tmpname_two .. " line 1: 'file two'",
+      })
+    end)
+  end)
+end)