#1117: Mock Popen in go_unknown_command test

Instead of ignoring it whenever `go` is unavailable

tests/rules/test_go_unknown_command.py

@@ -1,7 +1,7 @@
 import pytest
+from io import BytesIO
 from thefuck.rules.go_unknown_command import match, get_new_command
 from thefuck.types import Command
-from thefuck.utils import which
 
 
 @pytest.fixture
@@ -10,6 +10,65 @@ def build_misspelled_output():
 Run 'go help' for usage.'''
 
 
+@pytest.fixture
+def go_stderr(mocker):
+    stderr = b'''Go is a tool for managing Go source code.
+
+Usage:
+
+\tgo <command> [arguments]
+
+The commands are:
+
+\tbug         start a bug report
+\tbuild       compile packages and dependencies
+\tclean       remove object files and cached files
+\tdoc         show documentation for package or symbol
+\tenv         print Go environment information
+\tfix         update packages to use new APIs
+\tfmt         gofmt (reformat) package sources
+\tgenerate    generate Go files by processing source
+\tget         add dependencies to current module and install them
+\tinstall     compile and install packages and dependencies
+\tlist        list packages or modules
+\tmod         module maintenance
+\trun         compile and run Go program
+\ttest        test packages
+\ttool        run specified go tool
+\tversion     print Go version
+\tvet         report likely mistakes in packages
+
+Use "go help <command>" for more information about a command.
+
+Additional help topics:
+
+\tbuildconstraint build constraints
+\tbuildmode       build modes
+\tc               calling between Go and C
+\tcache           build and test caching
+\tenvironment     environment variables
+\tfiletype        file types
+\tgo.mod          the go.mod file
+\tgopath          GOPATH environment variable
+\tgopath-get      legacy GOPATH go get
+\tgoproxy         module proxy protocol
+\timportpath      import path syntax
+\tmodules         modules, module versions, and more
+\tmodule-get      module-aware go get
+\tmodule-auth     module authentication using go.sum
+\tmodule-private  module configuration for non-public modules
+\tpackages        package lists and patterns
+\ttestflag        testing flags
+\ttestfunc        testing functions
+
+Use "go help <topic>" for more information about that topic.
+
+'''
+    mock = mocker.patch('subprocess.Popen')
+    mock.return_value.stderr = BytesIO(stderr)
+    return mock
+
+
 def test_match(build_misspelled_output):
     assert match(Command('go bulid', build_misspelled_output))
 
@@ -18,6 +77,6 @@ def test_not_match():
     assert not match(Command('go run', 'go run: no go files listed'))
 
 
-@pytest.mark.skipif(not which('go'), reason='Skip if go executable not found')
+@pytest.mark.usefixtures('no_memoize', 'go_stderr')
 def test_get_new_command(build_misspelled_output):
     assert get_new_command(Command('go bulid', build_misspelled_output)) == 'go build'