determine-test-runners: fix parallel tests

Since these tests run in parallel, we want to minimise our reliance on
environment variables. Also, we need to make sure that different
examples write to different paths.

Library/Homebrew/test/dev-cmd/determine-test-runners_spec.rb

@@ -13,9 +13,10 @@ describe "brew determine-test-runners" do
   let(:linux_runner) { "ubuntu-22.04" }
   let(:all_runners) { ["11", "11-arm64", "12", "12-arm64", "13", "13-arm64", linux_runner] }
   let(:intel_runners) { all_runners.reject { |r| r.end_with? "-arm64" } }
-  let(:arm64_runners) { all_runners.select { |r| r.end_with? "-arm64" } }
+  let(:arm64_runners) { all_runners - intel_runners }
   let(:macos_runners) { all_runners - [linux_runner] }
-  let(:github_output) { "#{TEST_TMPDIR}/github_output" }
+  # We need to make sure we write to a different path for each example.
+  let(:github_output) { "#{TEST_TMPDIR}/github_output#{TestRunnerTestHelper.new.number}" }
   let(:ephemeral_suffix) { "-12345-1" }
   let(:runner_env) do
     {
@@ -23,7 +24,6 @@ describe "brew determine-test-runners" do
       "HOMEBREW_LINUX_CLEANUP" => "false",
       "GITHUB_RUN_ID"          => ephemeral_suffix.split("-").second,
       "GITHUB_RUN_ATTEMPT"     => ephemeral_suffix.split("-").third,
-      "GITHUB_OUTPUT"          => github_output,
     }
   end
 
@@ -35,26 +35,10 @@ describe "brew determine-test-runners" do
       .and be_a_failure
   end
 
-  it "fails when the necessary environment variables are missing", :integration_test, :needs_linux do
-    setup_test_formula "testball"
-
-    runner_env.each_key do |k|
-      next if ["GITHUB_RUN_ID", "GITHUB_RUN_ATTEMPT"].include? k
-
-      runner_env_dup = runner_env.dup
-      runner_env_dup.delete(k)
-
-      expect { brew "determine-test-runners", "testball", runner_env_dup }
-        .to not_to_output.to_stdout
-        .and output("Error: #{k} is not defined\n").to_stderr
-        .and be_a_failure
-    end
-  end
-
   it "assigns all runners for formulae without any requirements", :integration_test, :needs_linux do
     setup_test_formula "testball"
 
-    expect { brew "determine-test-runners", "testball", runner_env }
+    expect { brew "determine-test-runners", "testball", runner_env.merge({ "GITHUB_OUTPUT" => github_output }) }
       .to not_to_output.to_stdout
       .and not_to_output.to_stderr
       .and be_a_success
@@ -64,7 +48,7 @@ describe "brew determine-test-runners" do
   end
 
   it "assigns all runners when there are deleted formulae", :integration_test, :needs_linux do
-    expect { brew "determine-test-runners", "", "testball", runner_env }
+    expect { brew "determine-test-runners", "", "testball", runner_env.merge({ "GITHUB_OUTPUT" => github_output }) }
       .to not_to_output.to_stdout
       .and not_to_output.to_stderr
       .and be_a_success
@@ -75,7 +59,7 @@ describe "brew determine-test-runners" do
 
   it "assigns `ubuntu-latest` when there are no testing formulae and no deleted formulae", :integration_test,
      :needs_linux do
-    expect { brew "determine-test-runners", "", runner_env }
+    expect { brew "determine-test-runners", "", runner_env.merge({ "GITHUB_OUTPUT" => github_output }) }
       .to not_to_output.to_stdout
       .and not_to_output.to_stderr
       .and be_a_success
@@ -90,7 +74,7 @@ describe "brew determine-test-runners" do
       depends_on arch: :x86_64
     RUBY
 
-    expect { brew "determine-test-runners", "intel_depender", runner_env }
+    expect { brew "determine-test-runners", "intel_depender", runner_env.merge({ "GITHUB_OUTPUT" => github_output }) }
       .to not_to_output.to_stdout
       .and not_to_output.to_stderr
       .and be_a_success
@@ -105,7 +89,9 @@ describe "brew determine-test-runners" do
       depends_on arch: :arm64
     RUBY
 
-    expect { brew "determine-test-runners", "fancy-m1-ml-framework", runner_env }
+    expect do
+      brew "determine-test-runners", "fancy-m1-ml-framework", runner_env.merge({ "GITHUB_OUTPUT" => github_output })
+    end
       .to not_to_output.to_stdout
       .and not_to_output.to_stderr
       .and be_a_success
@@ -120,7 +106,7 @@ describe "brew determine-test-runners" do
       depends_on :macos
     RUBY
 
-    expect { brew "determine-test-runners", "xcode-helper", runner_env }
+    expect { brew "determine-test-runners", "xcode-helper", runner_env.merge({ "GITHUB_OUTPUT" => github_output }) }
       .to not_to_output.to_stdout
       .and not_to_output.to_stderr
       .and be_a_success
@@ -135,7 +121,9 @@ describe "brew determine-test-runners" do
       depends_on :linux
     RUBY
 
-    expect { brew "determine-test-runners", "linux-kernel-requirer", runner_env }
+    expect do
+      brew "determine-test-runners", "linux-kernel-requirer", runner_env.merge({ "GITHUB_OUTPUT" => github_output })
+    end
       .to not_to_output.to_stdout
       .and not_to_output.to_stderr
       .and be_a_success
@@ -151,7 +139,7 @@ describe "brew determine-test-runners" do
       depends_on macos: :ventura
     RUBY
 
-    expect { brew "determine-test-runners", "needs-macos-13", runner_env }
+    expect { brew "determine-test-runners", "needs-macos-13", runner_env.merge({ "GITHUB_OUTPUT" => github_output }) }
       .to not_to_output.to_stdout
       .and not_to_output.to_stderr
       .and be_a_success
@@ -162,14 +150,25 @@ describe "brew determine-test-runners" do
   end
 end
 
-def parse_runner_hash(file)
+def get_runners(file)
   runner_line = File.open(file).first
   json_text = runner_line[/runners=(.*)/, 1]
-  JSON.parse(json_text)
+  runner_hash = JSON.parse(json_text)
-end
-
-def get_runners(file)
-  runner_hash = parse_runner_hash(file)
   runner_hash.map { |item| item["runner"].delete_suffix(ephemeral_suffix) }
              .sort
 end
+
+class TestRunnerTestHelper
+  @instances = 0
+
+  class << self
+    attr_accessor :instances
+  end
+
+  attr_reader :number
+
+  def initialize
+    self.class.instances += 1
+    @number = self.class.instances
+  end
+end