Prioritize PARALLEL_RAILS_ENV over the standard (#1019)

* Prioritize PARALLEL_RAILS_ENV over RAILS_ENV

* RSpec tests

* Update CHANGELOG.md

* Add doc in Readme.md

* Add a reference to #776 in the changelog

* Adapt the code based on @grosser's suggestion

#1019 (review)

Author: mfilipe

CHANGELOG.md

@@ -8,6 +8,8 @@ only add here if you are working on a PR
 
 ### Added
 
+- Rake tasks will prioritize the `PARALLEL_RAILS_ENV` value over the default `test` environment
+
 ### Fixed
 
 ## 5.3.1 - 2025-07-23

Readme.md

@@ -360,6 +360,7 @@ TIPS
  - Debug errors that only happen with multiple files using `--verbose` and [cleanser](https://github.com/grosser/cleanser)
  - `export PARALLEL_TEST_PROCESSORS=13` to override default processor count
  - `export PARALLEL_TEST_MULTIPLY_PROCESSES=.5` to override default processor multiplier
+ - `export PARALLEL_RAILS_ENV=environment_name` to override the default `test` environment
  - Shell alias: `alias prspec='parallel_rspec -m 2 --'`
  - [Spring] Add the [spring-commands-parallel-tests](https://github.com/DocSpring/spring-commands-parallel-tests) gem to your `Gemfile` to get `parallel_tests` working with Spring.
  - `--first-is-1` will make the first environment be `1`, so you can test while running your full suite.<br/>

lib/parallel_tests/tasks.rb

@@ -6,7 +6,7 @@ module ParallelTests
   module Tasks
     class << self
       def rails_env
-        'test'
+        ENV['PARALLEL_RAILS_ENV'] || 'test'
       end
 
       def load_lib

spec/parallel_tests/tasks_spec.rb

@@ -42,13 +42,13 @@
   end
 
   describe ".rails_env" do
-    it "should be test" do
+    it "should be test when nothing was set" do
       expect(ParallelTests::Tasks.rails_env).to eq("test")
     end
 
-    it "should disregard whatever was set" do
-      ENV["RAILS_ENV"] = "foo"
-      expect(ParallelTests::Tasks.rails_env).to eq("test")
+    it "should prioritize the PARALLEL_RAILS_ENV value over the standard" do
+      ENV["PARALLEL_RAILS_ENV"] = "bar"
+      expect(ParallelTests::Tasks.rails_env).to eq("bar")
     end
   end