Write partial results on failure

Previously if a command failed you lose the resulting doc, including everything up to that point which might be salvalgable. With this change a partial result is written to disk on failure.

lib/rundoc/cli.rb

@@ -190,6 +190,8 @@ def call
         from: execution_context.output_dir,
         to: on_failure_dir
       )
+
+      on_failure_dir.join("RUNDOC_FAILED.md").write(Rundoc::CodeSection.partial_result_to_doc)
     end
 
     private def on_success(output)

lib/rundoc/code_section.rb

@@ -84,6 +84,10 @@ def render
       self.class.to_doc(result: result, env: env)
     end
 
+    def self.partial_result_to_doc
+      self.to_doc(result: PARTIAL_RESULT, env: PARTIAL_ENV)
+    end
+
     def self.to_doc(result: , env: )
       array = [env[:before]]
 

test/integration/failure_test.rb

@@ -0,0 +1,46 @@
+require "test_helper"
+
+class IntegrationFailureTest < Minitest::Test
+  def test_writes_to_dir_on_failure
+    Dir.mktmpdir do |dir|
+      Dir.chdir(dir) do
+        dir = Pathname(dir)
+
+        source_path = dir.join("RUNDOC.md")
+        source_path.write <<~EOF
+          ```
+          :::>> $ mkdir lol
+          :::>> $ touch lol/rofl.txt
+          :::>> $ touch does/not/exist.txt
+          ```
+        EOF
+
+        io = StringIO.new
+
+        error = nil
+        begin
+          Rundoc::CLI.new(
+            io: io,
+            source_path: source_path,
+            on_success_dir: dir.join(SUCCESS_DIRNAME)
+          ).call
+        rescue => e
+          error = e
+        end
+
+        assert error
+        assert_includes error.message, "exited with non zero status"
+
+        refute dir.join(SUCCESS_DIRNAME).join("lol").exist?
+        refute dir.join(SUCCESS_DIRNAME).join("lol").join("rofl.txt").exist?
+
+        assert dir.join(FAILURE_DIRNAME).join("lol").exist?
+        assert dir.join(FAILURE_DIRNAME).join("lol").join("rofl.txt").exist?
+
+        doc = dir.join(FAILURE_DIRNAME).join("RUNDOC_FAILED.md").read
+        assert_includes doc, "$ mkdir lol"
+        assert_includes doc, "$ touch lol/rofl.txt"
+      end
+    end
+  end
+end