Please specify the exact commands and sourcecode used to reproduce the error.
From the issue filed its unclear where go test was run and with which code.

I think this is working as intended: module paths may not contain the character →. I've copied the full list of requirements below.

If none of the module or package paths in this build actually contain the → character, please add enough information for us to reproduce the problem, and we can reopen this and investigate.

A module path must satisfy the following requirements:

• The path must consist of one or more path elements separated by slashes
  (/, U+002F). It must not begin or end with a slash.
• Each path element is a non-empty string made of up ASCII letters, ASCII
  digits, and limited ASCII punctuation (+, -, ., _, and ~).
• A path element may not begin or end with a dot (., U+002E).
• The element prefix up to the first dot must not be a reserved file name on
  Windows, regardless of case (CON, com1, NuL, and so on).

If the module path appears in a require directive and is not replaced, or
if the module paths appears on the right side of a replace directive,
the go command may need to download modules with that path, and some
additional requirements must be satisfied.

• The leading path element (up to the first slash, if any), by convention a
  domain name, must contain only lower-case ASCII letters, ASCII digits, dots
  (., U+002E), and dashes (-, U+002D); it must contain at least one dot and
  cannot start with a dash.
• For a final path element of the form /vN where N looks numeric (ASCII
  digits and dots), N must not begin with a leading zero, must not be /v1,
  and must not contain any dots.
  • For paths beginning with gopkg.in/, this requirement is replaced by a
    requirement that the path follow the gopkg.in service's
    conventions.