Add support for re-usable containers

[devuo]

Add support for developers to pass gnomock.WithContainerReuse() option that makes Gnomock attempt to re-use an already running container with the name specified via gnomock.WithContainerName().

If the container with the given name does not exist, or if it uses a different image than the one configured, the normal flow of Gnomock is used, namely a new container is created in case it doesn't exist, or replaced if using a different image.

Pending:

• Agree on technical solution
• Add inline comments
• Write tests

[devuo]

Related with #691

[devuo]

@orlangure do you agree with the approach I followed? If yes, I'll add the comments and tests and put it to review.

[orlangure]

Very cool!

I like the idea to keep the existing behaviour unless the other option is specified, and I really like the extra bit you added with the image match: if the image changed, no need to reuse the container, it needs to be created again.

I looked at the code briefly, and all looks good. I think there might be a problem with "running" filter you used to list the containers: if there is a container with the same name that is not "running", we will try to create a new one with the same name and fail (I guess that's what would happen). Please look a bit more into that potential issue, or confirm that the behaviour will be as expected with the existing code.

[devuo]

@orlangure tried to reproduce the problem but was unable to. For two reasons:

• The first is that the containers Gnomock creates have auto remove, then once they exit they are removed:

  gnomock/docker.go

  Line 302 in 5e86a8b

  AutoRemove: true,

• The second because Gnomock is already handling the case of duplicate containers:

  gnomock/docker.go

  Lines 312 to 324 in 5e86a8b

  	matches := duplicateContainerRegexp.FindStringSubmatch(err.Error())
  	if len(matches) == 2 {
  	d.log.Infow("duplicate container found, stopping", "container", matches[1])
  	err = d.client.ContainerRemove(ctx, matches[1], types.ContainerRemoveOptions{
  	Force: true,
  	})
  	if err != nil {
  	return nil, fmt.Errorf("can't remove existing container: %w", err)
  	}
  	resp, err = d.client.ContainerCreate(ctx, containerConfig, hostConfig, nil, nil, cfg.ContainerName)
  	}

[devuo]

@orlangure also added tests. The only test I did not add was for the "replacement scenario" (the one where the image mismatches) and that was because I didn't know which image to use other than docker.io/orlangure/gnomock-test-image.

[codecov-commenter]

Codecov Report

Base: 85.88% // Head: 85.80% // Decreases project coverage by -0.08% ⚠️

Coverage data is based on head (5f72952) compared to base (5e86a8b).
Patch coverage: 80.48% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #693      +/-   ##
==========================================
- Coverage   85.88%   85.80%   -0.09%     
==========================================
  Files          49       49              
  Lines        2281     2310      +29     
==========================================
+ Hits         1959     1982      +23     
- Misses        167      170       +3     
- Partials      155      158       +3     

Impacted Files	Coverage Δ
docker.go	89.47% <78.94%> (-0.63%)	⬇️
options.go	100.00% <100.00%> (ø)
preset/postgres/preset.go	84.21% <0.00%> (-2.64%)	⬇️

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[devuo]

@orlangure fixed lint issues, should be ok now

[orlangure]

@devuo, thank you so much for working on it, and for the last sidecar touch as well 😼
I'm a bit short on time to prepare a new release, and will try to work on in ASAP, maybe tonight or during the weekend.

[orlangure]

Perfect 😼
Thank you.