Add SystemCommand::Result#merged_output.

Library/Homebrew/system_command.rb

@@ -185,6 +185,11 @@ class SystemCommand
                          .join
     end
 
+    def merged_output
+      @merged_output ||= @output.map { |_, line| line }
+                                .join
+    end
+
     def success?
       @exit_status.zero?
     end

Library/Homebrew/test/system_command_result_spec.rb

@@ -1,32 +1,47 @@
 require "system_command"
 
 describe SystemCommand::Result do
-  describe "#to_ary" do
-    let(:output) {
-      [
-        [:stdout, "output"],
-        [:stderr, "error"],
-      ]
-    }
-    subject(:result) {
-      described_class.new([], output, instance_double(Process::Status, exitstatus: 0, success?: true))
-    }
+  let(:output_array) {
+    [
+      [:stdout, "output\n"],
+      [:stderr, "error\n"],
+    ]
+  }
+  subject(:result) {
+    described_class.new([], output_array, instance_double(Process::Status, exitstatus: 0, success?: true))
+  }
 
+  describe "#to_ary" do
     it "can be destructed like `Open3.capture3`" do
       out, err, status = result
 
-      expect(out).to eq "output"
-      expect(err).to eq "error"
+      expect(out).to eq "output\n"
+      expect(err).to eq "error\n"
       expect(status).to be_a_success
     end
   end
 
-  describe "#plist" do
-    subject {
-      described_class.new(command, [[:stdout, stdout]], instance_double(Process::Status, exitstatus: 0)).plist
-    }
+  describe "#stdout" do
+    it "returns the standard output" do
+      expect(result.stdout).to eq "output\n"
+    end
+  end
 
-    let(:command) { ["true"] }
+  describe "#stderr" do
+    it "returns the standard error output" do
+      expect(result.stderr).to eq "error\n"
+    end
+  end
+
+  describe "#merged_output" do
+    it "returns the combined standard and standard error output" do
+      expect(result.merged_output).to eq "output\nerror\n"
+    end
+  end
+
+  describe "#plist" do
+    subject { result.plist }
+    let(:output_array) { [[:stdout, stdout]] }
     let(:garbage) {
       <<~EOS
         Hello there! I am in no way XML am I?!?!