Add specs for Mutant.isolate

lib/mutant.rb

@@ -62,7 +62,7 @@ module Mutant
     begin
       data = Marshal.load(reader.read)
     rescue ArgumentError
-      raise IsolationError, 'Childprocess wrote unmarshallable data'
+      raise IsolationError, 'Childprocess wrote un-unmarshallable data'
     end
 
     status = Process.waitpid2(pid).last

spec/unit/mutant_spec.rb

@@ -38,4 +38,55 @@ describe Mutant do
       expect(inspect).to be_frozen
     end
   end
+
+  describe '.isolate' do
+    let(:object) { described_class }
+
+    let(:expected_return) { :foo }
+
+    subject { object.isolate(&block) }
+
+    def redirect_stderr
+      $stderr = File.open('/dev/null')
+    end
+
+    context 'when block returns mashallable data, and process exists zero' do
+      let(:block) do
+        lambda do
+          :data_from_child_process
+        end
+      end
+
+      it { should eql(:data_from_child_process) }
+    end
+
+    context 'when block does return marshallable data' do
+      let(:block) do
+        lambda do
+          redirect_stderr
+          $stderr # not mashallable, nothing written to pipe and raised exceptions in child
+        end
+      end
+
+      it 'raises an exception' do
+        expect { subject }.to raise_error(Mutant::IsolationError, 'Childprocess wrote un-unmarshallable data')
+      end
+    end
+
+    context 'when block does return marshallable data, but process exits with nonzero exitstatus' do
+      let(:block) do
+        lambda do
+          redirect_stderr
+          at_exit do
+            raise
+          end
+          :foo
+        end
+      end
+
+      it 'raises an exception' do
+        expect { subject }.to raise_error(Mutant::IsolationError, 'Childprocess exited with nonzero exit status: 1')
+      end
+    end
+  end
 end