Allow for duplicate tests with --allow-duplicates (#940)

* Allow for duplicate tests to run

> tldr; It's useful to run 1 or more tests multiple times when debugging
and I'd like to propose an option to do so with parallel_tests

I often find that I'd like to run 1+ files locally, in parallel, to rule
out certain flakey test behaviors (order tests are being run). Kind of
like a form of "test fuzzing" I guess? The purpose is to generally rule
out the test is flakey.

I often find myself doing something like this in zsh:

    repeat 10 bin/rspec path/to/my_spec.rb

Sometimes it's more than 10, and sometimes it's more than 1 file I'd
like to run at the same time.

I'd like to do this with parallel_tests instead and I'd like to propose
this PR as a potential solution (I didn't see this functionality present
with the current options)

Example usage:

```
export TEST_FILES="
spec/test_1.rb
spec/test_1.rb
spec/test_1.rb
spec/test_1.rb
spec/test_1.rb
"

bin/spring parallel_rspec -n 5 --allow-duplicates -- $(echo $TEST_FILES)

bin/spring parallel_rspec -n 5 -- $(echo $TEST_FILES)
```

There's one _minor_ caveat:

These duplicates will still be unique per process because RSpec _also_
calls uniq in a couple places

[here](https://github.com/rspec/rspec-core/blob/1e661db5c5b431c0ee88a383e8e3767f02dccbfe/lib/rspec/core/configuration.rb#L2202), [here](https://github.com/rspec/rspec-core/blob/1e661db5c5b431c0ee88a383e8e3767f02dccbfe/lib/rspec/core/configuration.rb#L2222), and [here](https://github.com/rspec/rspec-core/blob/1e661db5c5b431c0ee88a383e8e3767f02dccbfe/lib/rspec/core/configuration.rb#L1636)

If there is interest in this PR, I'd be happy to propose a similar
PR to the RSpec team.

One other thought: I was also thinking a companion `--repeat <Integer>`
flag could be useful, where it multiplies the file list N times
and then builds the commands.

    bin/spring parallel_rspec --repeat 100 -- path/to/my_spec.rb

Would happy to hear any thoughts or opinions on that as well. I'd
be happy to do a separate PR

* Update lib/parallel_tests/test/runner.rb

Co-authored-by: Michael Grosser <michael@grosser.it>

* Rubocop cleanup

---------

Co-authored-by: Michael Grosser <michael@grosser.it>

CHANGELOG.md

@@ -1,6 +1,7 @@
 # Changelog
 
 ## Unreleased
+- Add `--allow-duplicates` flag to support re-running 1 spec multiple times
 
 ### Breaking Changes
 

Readme.md

@@ -279,6 +279,7 @@ Options are:
         --nice                       execute test commands with low priority.
         --runtime-log [PATH]         Location of previously recorded test runtimes
         --allowed-missing [INT]      Allowed percentage of missing runtimes (default = 50)
+        --allow-duplicates           When detecting files to run, allow duplicates. Useful for local debugging
         --unknown-runtime [FLOAT]    Use given number as unknown runtime (otherwise use average time)
         --first-is-1                 Use "1" as TEST_ENV_NUMBER to not reuse the default test environment
         --fail-fast                  Stop all groups when one group fails (best used with --test-options '--fail-fast' if supported

lib/parallel_tests/cli.rb

@@ -278,6 +278,7 @@ def parse_options!(argv)
         opts.on("--nice", "execute test commands with low priority.") { options[:nice] = true }
         opts.on("--runtime-log [PATH]", "Location of previously recorded test runtimes") { |path| options[:runtime_log] = path }
         opts.on("--allowed-missing [INT]", Integer, "Allowed percentage of missing runtimes (default = 50)") { |percent| options[:allowed_missing_percent] = percent }
+        opts.on('--allow-duplicates', 'When detecting files to run, allow duplicates') { options[:allow_duplicates] = true }
         opts.on("--unknown-runtime [FLOAT]", Float, "Use given number as unknown runtime (otherwise use average time)") { |time| options[:unknown_runtime] = time }
         opts.on("--first-is-1", "Use \"1\" as TEST_ENV_NUMBER to not reuse the default test environment") { options[:first_is_1] = true }
         opts.on("--fail-fast", "Stop all groups when one group fails (best used with --test-options '--fail-fast' if supported") { options[:fail_fast] = true }

lib/parallel_tests/test/runner.rb

@@ -238,8 +238,9 @@ def find_tests(tests, options = {})
           suffix_pattern = options[:suffix] || test_suffix
           include_pattern = options[:pattern] || //
           exclude_pattern = options[:exclude_pattern]
+          allow_duplicates = options[:allow_duplicates]
 
-          (tests || []).flat_map do |file_or_folder|
+          files = (tests || []).flat_map do |file_or_folder|
             if File.directory?(file_or_folder)
               files = files_in_folder(file_or_folder, options)
               files = files.grep(suffix_pattern).grep(include_pattern)
@@ -248,7 +249,9 @@ def find_tests(tests, options = {})
             else
               file_or_folder
             end
-          end.uniq
+          end
+
+          allow_duplicates ? files : files.uniq
         end
 
         def files_in_folder(folder, options = {})

spec/parallel_tests/cli_spec.rb

@@ -78,6 +78,10 @@ def call(*args)
         .to eq(defaults.merge(first_is_1: true))
     end
 
+    it "parses allow-duplicates" do
+      expect(call(["test", "--allow-duplicates"])).to eq(defaults.merge(allow_duplicates: true))
+    end
+
     context "parse only-group" do
       it "group_by should be set to filesize" do
         expect(call(["test", "--only-group", '1'])).to eq(defaults.merge(only_group: [1], group_by: :filesize))

spec/parallel_tests/test/runner_spec.rb

@@ -387,6 +387,10 @@ def call(*args)
     it "discards duplicates" do
       expect(call(['baz', 'baz'])).to eq(['baz'])
     end
+
+    it "keeps duplicates when allow_duplicates" do
+      expect(call(['baz', 'baz'], allow_duplicates: true)).to eq(['baz', 'baz'])
+    end
   end
 
   describe ".summarize_results" do