Add function to initialize a test workspace

[tcmoore3]

This is related to signac-flow issue glotzerlab/signac-flow#130 and glotzerlab/signac-flow#129, where we decided it makes more sense to break up the data space initialization into signac core and the flow project initialization into flow.

Types of Changes

• New feature

Checklist:

• I am familiar with the Contributing Guidelines.
• I agree with the terms of the Contributor Agreement.
• My name is on the list of contributors.
• My code follows the code style guideline of this project.
• The changes introduced by this pull request are covered by existing or newly introduced tests.

If necessary:

• I have updated the API documentation as part of the package doc-strings.
• I have created a separate pull request to update the framework documentation on signac-docs and linked it here.
• I have updated the changelog.

[codecov]

Codecov Report

Merging #215 into master will increase coverage by 0.09%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #215      +/-   ##
==========================================
+ Coverage   65.15%   65.25%   +0.09%     
==========================================
  Files          37       38       +1     
  Lines        5599     5615      +16     
==========================================
+ Hits         3648     3664      +16     
  Misses       1951     1951

Impacted Files	Coverage Δ
signac/testing.py	100% <100%> (ø)
signac/__init__.py	100% <100%> (ø)	⬆️

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[csadorf]

I'm going to add a few unit tests and then this is ready to ship.

[csadorf]

@tcmoore3 I've added a few comments with suggestions to keep track of things. I'm happy to take those on myself unless you want to do that. Just let me know.

[tcmoore3]

@csadorf Cool. I made the suggested changes. Did you already write unit tests? I didn't see them on the branch.

[csadorf]

@csadorf Cool. I made the suggested changes. Did you already write unit tests? I didn't see them on the branch.

No, I didn't get to it. Maybe you or someone else could write them?

[csadorf]

I'd like to extend the unit test just a little bit prior to merging, otherwise this is all good.

[csadorf]

I am going to try to fix issue #217 before merging this.

[tcmoore3]

LGTM