test: set cacheRoot on checksum download

[erickzhao]

Checklist

• I have read the contribution documentation for this project.
• I agree to follow the code of conduct that this project follows, as appropriate.
• The changes are appropriately documented (if applicable).
• The changes have sufficient test coverage (if applicable).
• The testsuite passes successfully on my local machine (if applicable).

Summary

Fixes #1421.

Our test-linux suite has had a very poor 52% success rate according to CircleCI insights. Each one of the Linux test suites seems to fail about 1/5 of the time.

Job Name	Total Credits	P95 Duration (seconds)	Runs	Success Rate
"test-linux-14"	517	227	17	0.82
"test-linux-16"	539	220	19	0.79
"test-linux-18"	542	271	16	0.81
"test-mac"	3031	329	15	1
"test-windows"	1974	272	17	0.88

The observed error was always the following:

Downloading Electron v1.4.13 before running tests...
Error: dest already exists.
    at /home/circleci/project/node_modules/@electron/get/node_modules/fs-extra/lib/move/move.js:41:31
    at /home/circleci/project/node_modules/@electron/get/node_modules/universalify/index.js:23:46

Exited with code exit status 1

This error occurred in our test setup code, which downloads Electron with @electron/get before running the test suite. During this setup process, we download the checksum first as of commit 621560b.

To investigate, I added the DEBUG=@electron/get* environment variable in CI to get verbose debug logging. Two things seem to be occurring:

1. The initial checksum download is set without a cache folder, so it never gets written to the cache after being downloaded.

Downloading Electron v1.4.13 before running tests...
  @electron/get:index Checking the cache (undefined) for SHASUMS256.txt (https://github.com/electron/electron/releases/download/v1.4.13/SHASUMS256.txt) +0ms
  @electron/get:index Cache miss +3ms

2. The setup process downloads the SHASUM256.txt checksums with cache misses for each binary. Since these downloads are done in parallel, the filesystem operations run into a race condition:

  @electron/get:cache Moving /tmp/electron-download-gaC39r/SHASUMS256.txt to /home/circleci/.electron/4660c2617dcac48c05988e181e4f7ff85132cd278bba79561816d3e7da1cc50c/SHASUMS256.txt +12ms
  @electron/get:cache * Replacing existing file +0ms
  @electron/get:cache Moving /tmp/electron-download-mSMl8f/SHASUMS256.txt to /home/circleci/.electron/4660c2617dcac48c05988e181e4f7ff85132cd278bba79561816d3e7da1cc50c/SHASUMS256.txt +7ms
  @electron/get:cache Moving /tmp/electron-download-oB433U/SHASUMS256.txt to /home/circleci/.electron/4660c2617dcac48c05988e181e4f7ff85132cd278bba79561816d3e7da1cc50c/SHASUMS256.txt +12ms
  @electron/get:cache * Replacing existing file +1ms
  @electron/get:cache Moving /tmp/electron-download-SeHepQ/SHASUMS256.txt to /home/circleci/.electron/4660c2617dcac48c05988e181e4f7ff85132cd278bba79561816d3e7da1cc50c/SHASUMS256.txt +18ms
Error: dest already exists.
    at /home/circleci/project/node_modules/@electron/get/node_modules/fs-extra/lib/move/move.js:41:31
    at /home/circleci/project/node_modules/@electron/get/node_modules/universalify/index.js:23:46

Fix

To fix this, I set a cacheRoot on the initial SHASUM256.txt download so that we get cache hits when downloading the checksums during the binary download. I'm assuming this is the right fix since we must have pre-downloaded the checksums for a reason.

Evaluation

I got CI to pass 10x in a row! With the 52% success rate, this had a 0.145% chance of happening.

[codecov]

Codecov Report

Merging #1540 (628fedb) into main (6430d3f) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #1540   +/-   ##
=======================================
  Coverage   95.58%   95.58%           
=======================================
  Files          15       15           
  Lines         793      793           
=======================================
  Hits          758      758           
  Misses         35       35           

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[malept]

Seems good