fix(core-library): do not create pr when a pr already exists for a ref

[TomKristie]

Recall that GitHub PRs just point to a reference head which are applied on-top of some base reference head, typically master, and so when the reference gets updated the PR automatically gets updated as well.

There may be scenarios where a pull request is already created for a ref, and a user will re-invoke code-suggester create pr using the same ref. If the force flag/parameter is true, a new ref is not created. Instead code-suggester create pr will force-update the existing reference. If we try to re-create the a pr for the same reference, there will be a duplication issue. Hence, if there is an existing pr, just update the ref, and GitHub will just adjust UI display accordingly to the reference HEAD data. However, if force flag/parameter is false, code-suggester create pr will fail when trying to create the reference because there is a duplicate reference.

TL;DR
When there is an existing pr for the a reference and code-suggester create pr is re-invoked, do not create a new pr. Instead, re-use the old one and update the ref.

Closes #17

[codecov]

Codecov Report

Merging #66 into master will increase coverage by 0.15%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #66      +/-   ##
==========================================
+ Coverage   85.96%   86.11%   +0.15%     
==========================================
  Files          14       14              
  Lines        1190     1203      +13     
  Branches       83       81       -2     
==========================================
+ Hits         1023     1036      +13     
  Misses        166      166              
  Partials        1        1              

Impacted Files	Coverage Δ
src/github-handler/fork-handler.ts	98.03% <ø> (-0.04%)	⬇️
src/github-handler/pull-request-handler.ts	100.00% <100.00%> (ø)

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[chingor13]

So this handles the case when essentially there is an existing branch. Is this not the same case as the force option?

[TomKristie]

So this handles the case when essentially there is an existing branch. Is this not the same case as the force option?

Correct. Basically if there is an existing PR for the branch, do not create a new PR, re-use the old one. GitHub PRs just point to a reference head which are applied on-top of some reference head, typically master, and so when the reference gets updated the PR automatically gets updated as well.

[chingor13]

You can nest describe blocks - many of these tests share the same setup for the case of an already existing PR.

describe('when there are similar refs with pull requests open', async () => {
  beforeEach(() => {
    // set up sinon for list pull request
  });
  it('should create another pull request if it's not the exact ref', async () => {

  });
});

[chingor13]

This should be already handled by the outer describe blocks's afterEach which is restoring the sandbox.