[ggj][infra][3/5] feat: implement update golden bazel rules for dummy test

[xiaozhenliu-gg5]

Find more details in design doc: go/java-micro-file-diff-infra

1. Added rules_bazel/java_diff_test.bzl where update_golden bazel rule is defined, including two parts: running JUnit test and overwritting goldens.
2. Added SingleJUnitTestRunner which helps us to manually trigger the JUnit test, it takes test_class_name as arg and emits test result if any failure is detected.
3. Added Utils.java in test/framework which helps to save the generated code from JUnit test to tmp file in folder $TEST_OUTPUT_HOME. System environment is set to interact with update golden bazel rules, the folder will get deleted once the bazel rules finish.
4. update_golden rule is called from BUILD.bazel in dummy test, and junit_runner_binary is defined for running the JUnit test when updating goldens.

How we use it (check out this branch and modify the dummy/goldens/*.golden)

> bazel test //...
Tests have failures: [classWithHeader(com.google.api.generator.gapic.dummy.FileDiffInfraDummyTest): Differences found: 
--- golden
+++ codegen
@@ -17,3 +17,3 @@
 package com.google.showcase.v1beta1.stub;
 
-public class  {}
+public class EchoStubSettings {}]
//src/test/java/com/google/api/generator/gapic/dummy:FileDiffInfraDummyTest FAILED in 5.6s
  /private/var/tmp/_bazel_xiaozhenliu/27d546162d4fdfcb8b9c40b4c5bf4971/execroot/com_google_api_codegen/bazel-out/darwin-fastbuild/testlogs/src/test/java/com/google/api/generator/gapic/dummy/FileDiffInfraDummyTest/test.log


> bazel run //src/test/java/com/google/api/generator/gapic/dummy:FileDiffInfraDummyTest_update
> bazel test //...
.....
Executed 53 out of 66 tests: 66 tests pass.

Next step would be:

1. Move the existing expected class string to file-diff infra, including
   (a)gapic/composer/*Test.
   (b)engine/astIntegrationTest
2. Update developer doc to include this instruction for updating goldens.

[vam-google]

It looks good. I left quite a few comments, but most of them are minor and/or optional.

My only real concern is the general structure of the BUILD.bazel files (if we don't be careful here, we may end up in a very verbose layout, with many BUILD files everywhere and many targets being redeclared in each BUILD file, which will be very difficult to maintain).

[miraleung]

It looks good. I left quite a few comments, but most of them are minor and/or optional.

My only real concern is the general structure of the BUILD.bazel files (if we don't be careful here, we may end up in a very verbose layout, with many BUILD files everywhere and many targets being redeclared in each BUILD file, which will be very difficult to maintain).

The motivation for the BUILD file structure in this repo is to keep individual repos self-contained (following google3 style), so the proliferation of files is fine.

Otherwise +1 to Vadym's comments below.

[miraleung]

From a clean client, I tried running this update command, and got the error below, plus lots of warnings. Seems that this isn't working and requires each incremental target to be built first, whereas it should all just work with bazel run. I'll fix these issues too.

bazel run //src/test/java/com/google/api/generator/gapic/dummy:FileDiffInfraDummyTest_update

Target //src/test/java/com/google/api/generator/gapic/dummy:FileDiffInfraDummyTest_update up-to-date:
  bazel-bin/src/test/java/com/google/api/generator/gapic/dummy/FileDiffInfraDummyTest_update.sh
INFO: Elapsed time: 8.211s, Critical Path: 0.06s
INFO: 0 processes.
INFO: Build completed successfully, 4 total actions
INFO: Build completed successfully, 4 total actions
unzip:  cannot find or open bazel-out/k8-fastbuild/bin/src/test/java/com/google/api/generator/gapic/dummy/FileDiffInfraDummyTest_update_output.zip, bazel-out/k8-fastbuild/bin/src/test/java/com/google/api/generator/gapic/dummy/FileDiffInfraDummyTest_update_output.zip.zip or bazel-out/k8-fastbuild/bin/src/test/java/com/google/api/generator/gapic/dummy/FileDiffInfraDummyTest_update_output.zip.ZIP.

[miraleung]

Another one I found: In a clean client, I get this error, even though it updates fine:

Error occurs when reading golden file

[miraleung]

Fixed all of these in #363.

[xiaozhenliu-gg5]

This implementation was based on the prerequisites of users running bazel test or bazel build first before updating any goldens files. The usage was described in the description, but it does not support directly bazel run testTarget_update for updating goldens before any test run.
Error occurs when reading golden file only happens when not finding/reading the goldens files, I did not have chance to repro that error, but thanks for the refactor to allow the direct usage of update_goldens.