1 files changed, 17 insertions, 6 deletions
diff --git a/test/helpers.lua b/test/helpers.lua
index c2a708197f..ebc0a7d811 100644
--- a/test/helpers.lua
+++ b/test/helpers.lua
@@ -73,12 +73,23 @@ function module.matches(pat, actual)
   end
   error(string.format('Pattern does not match.\nPattern:\n%s\nActual:\n%s', pat, actual))
 end
--- Expect an error matching pattern `pat`.
-function module.expect_err(pat, ...)
-  local fn = select(1, ...)
-  local fn_args = {...}
-  table.remove(fn_args, 1)
-  assert.error_matches(function() return fn(unpack(fn_args)) end, pat)
+
+-- Invokes `fn` and returns the error string, or raises an error if `fn` succeeds.
+--
+-- Usage:
+--    -- Match exact string.
+--    eq('e', pcall_err(function(a, b) error('e') end, 'arg1', 'arg2'))
+--    -- Match Lua pattern.
+--    matches('e[or]+$', pcall_err(function(a, b) error('some error') end, 'arg1', 'arg2'))
+--
+function module.pcall_err(fn, ...)
+  assert(type(fn) == 'function')
+  local status, rv = pcall(fn, ...)
+  if status == true then
+    error('expected failure, but got success')
+  end
+  local errmsg = tostring(rv):gsub('^[^:]+:%d+: ', '')
+  return errmsg
 end
 
 -- initial_path:  directory to recurse into