wire: make Vendor test work with Go module (google/go-cloud#469)

internal/wire/testdata/Vendor/bar/dummy.go

@@ -1,16 +0,0 @@
-// Copyright 2018 The Go Cloud Authors
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-//
-//     https://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-
-// Package bar is left intentionally blank.
-package bar

internal/wire/wire_test.go

@@ -72,10 +72,6 @@ func TestWire(t *testing.T) {
 	for _, test := range tests {
 		test := test
 		t.Run(test.name, func(t *testing.T) {
-			if test.name == "Vendor" && os.Getenv("GO111MODULE") != "off" {
-				// TODO: Remove the GO111MODULE check when it is not relevant (maybe after Go 1.12).
-				t.Skip("Skipped testing for vendored package for Go module turned on, see https://github.com/google/go-cloud/issues/326")
-			}
 			t.Parallel()
 
 			// Run Wire from a fake build context.
@@ -167,7 +163,11 @@ func goBuildCheck(test *testCase, wd string, bctx *build.Context, gen []byte) er
 		ReleaseTags: bctx.ReleaseTags,
 	}
 	buildDir := filepath.Join(gopath, "src", genPkg.ImportPath)
-	if err := runGo(realBuildCtx, buildDir, "build", "-o", testExePath); err != nil {
+	buildCmd := []string{"build", "-o", testExePath}
+	if test.name == "Vendor" && os.Getenv("GO111MODULE") == "on" {
+		buildCmd = append(buildCmd, "-mod=vendor")
+	}
+	if err := runGo(realBuildCtx, buildDir, buildCmd...); err != nil {
 		return fmt.Errorf("build: %v", err)
 	}