Replace manual mock generation with go generate

.travis.yml

@@ -29,6 +29,8 @@ before_script:
   # Install dependencies for testing.
   - go get github.com/golang/mock/gomock@v1.2.0
   - go get github.com/golang/mock/mockgen@v1.2.0
+  # Generate the mocks for testing.
+  - go generate ./...
 
 script:
   - make test

Makefile

@@ -25,13 +25,8 @@ gofmt_test:
 	$(VERB) echo "Running 'go fmt' test ..."
 	$(VERB) ./gofmt_test.sh
 
-ghutil_test:
-	$(VERB) echo
-	$(VERB) echo "Running tests in 'ghutil' recursively ..."
-	$(VERB) $(MAKE) VERBOSE=$(VERBOSE) -s -C ghutil test
-
 go_mod_tidy_test:
 	$(VERB) echo "Running 'go mod tidy' test ..."
 	$(VERB) ./go_mod_tidy_test.sh
 
-test: go_test gofmt_test ghutil_test go_mod_tidy_test
+test: go_test gofmt_test go_mod_tidy_test

README.md

@@ -50,27 +50,26 @@ $ go get github.com/golang/mock/gomock@v1.2.0
 $ go get github.com/golang/mock/mockgen@v1.2.0
 ```
 
+Generate the mocks:
+
+```bash
+$ go generate ./...
+```
+
 This specific version of both `gomock` and `mockgen` tools is what's used in
 this repo, and tests will fail if your version of these tools generates
 different code, including comments.
 
 To update the versions of these tools used in this repo:
 
-1. update the version numbers in this file (above) and in
-   [`.travis.yml`](.travis.yml) to match
-1. run the commands above to get those specific versions of the tools
-1. update the generated code in this repo via:
-
-   ```bash
-   $ cd ghutil
-   $ rm -f mock_ghutil.go
-   $ make mock
-   ```
-
+1. update the version numbers in this file (above) as well as in
+   [`.travis.yml`](.travis.yml) and [`go.mod`](go.mod) to match
+1. run `go mod tidy` to update the `go.sum` file
+1. run the updated `go get` commands above to get newer versions of the tools
+1. run the `go generate` command above to regenerate the mocks
 1. [run the tests](#testing) from the top-level of the tree
-1. commit your changes to this file (`README.md`), `.travis.yml`, and
-   `ghutil/mock_ghutil.go` and make sure the build passes on Travis CI before
-   merging the change
+1. commit your changes to this file (`README.md`) and `.travis.yml`, making
+   sure that the build passes on Travis CI before merging the change
 
 ## Testing
 

ghutil/.gitignore

@@ -0,0 +1 @@
+mock_ghutil.go

ghutil/ghutil.go

@@ -12,6 +12,10 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+// TODO(mbrukman): in the future, consider using the recently-added
+// `-copyright_filename` flag: https://github.com/golang/mock/pull/234
+
+//go:generate mockgen -source ghutil.go -destination mock_ghutil.go -package ghutil
 package ghutil
 
 import (