patch 8.2.1632: not checking the context of test_fails()

Problem:    Not checking the context of test_fails().
Solution:   Add the line number and context arguments.  Give error if
            assert_fails() argument types are wrong.
diff --git a/src/testdir/test_assert.vim b/src/testdir/test_assert.vim
index 1a18799..47dcc1f 100644
--- a/src/testdir/test_assert.vim
+++ b/src/testdir/test_assert.vim
@@ -269,6 +269,20 @@
     let exp = v:exception
   endtry
   call assert_match("E856: assert_fails() second argument", exp)
+
+  try
+    call assert_equal(1, assert_fails('xxx', 'E492', '', 'burp'))
+  catch
+    let exp = v:exception
+  endtry
+  call assert_match("E1115: assert_fails() fourth argument must be a number", exp)
+
+  try
+    call assert_equal(1, assert_fails('xxx', 'E492', '', 54, 123))
+  catch
+    let exp = v:exception
+  endtry
+  call assert_match("E1116: assert_fails() fifth argument must be a string", exp)
 endfunc
 
 func Test_assert_fails_in_try_block()