diff --git a/spec/unit/mutant/env_spec.rb b/spec/unit/mutant/env_spec.rb
index b400f116..a808d87e 100644
--- a/spec/unit/mutant/env_spec.rb
+++ b/spec/unit/mutant/env_spec.rb
@@ -14,13 +14,13 @@ RSpec.describe Mutant::Env do
     end
 
     let(:integration)       { instance_double(Mutant::Integration)     }
-    let(:context)           { instance_double(Mutant::Context)         }
     let(:test_a)            { instance_double(Mutant::Test)            }
     let(:test_b)            { instance_double(Mutant::Test)            }
     let(:tests)             { [test_a, test_b]                         }
     let(:selector)          { instance_double(Mutant::Selector)        }
     let(:integration_class) { Mutant::Integration::Null                }
     let(:isolation)         { instance_double(Mutant::Isolation::Fork) }
+    let(:mutation_subject)  { instance_double(Mutant::Subject)         }
 
     let(:mutation) do
       instance_double(
@@ -37,15 +37,6 @@ RSpec.describe Mutant::Env do
       )
     end
 
-    let(:mutation_subject) do
-      instance_double(
-        Mutant::Subject,
-        context:        context,
-        identification: 'subject',
-        source:         'original'
-      )
-    end
-
     subject { object.kill(mutation) }
 
     shared_examples_for 'mutation kill' do
@@ -68,12 +59,7 @@ RSpec.describe Mutant::Env do
     end
 
     context 'when isolation does not raise error' do
-      let(:test_result) do
-        instance_double(
-          Mutant::Result::Test,
-          passed: false
-        )
-      end
+      let(:test_result) { instance_double(Mutant::Result::Test) }
 
       before do
         expect(isolation).to receive(:call)
diff --git a/spec/unit/mutant/result/env_spec.rb b/spec/unit/mutant/result/env_spec.rb
index e6900408..22d9bd78 100644
--- a/spec/unit/mutant/result/env_spec.rb
+++ b/spec/unit/mutant/result/env_spec.rb
@@ -10,16 +10,11 @@ RSpec.describe Mutant::Result::Env do
   let(:env) do
     instance_double(
       Mutant::Env,
-      config:    config,
       subjects:  [instance_double(Mutant::Subject)],
       mutations: [instance_double(Mutant::Mutation)]
     )
   end
 
-  let(:config) do
-    instance_double(Mutant::Config)
-  end
-
   let(:subject_result) do
     instance_double(
       Mutant::Result::Subject,
diff --git a/spec/unit/mutant/result/mutation_spec.rb b/spec/unit/mutant/result/mutation_spec.rb
index bca9dd18..baef27d1 100644
--- a/spec/unit/mutant/result/mutation_spec.rb
+++ b/spec/unit/mutant/result/mutation_spec.rb
@@ -6,13 +6,7 @@ RSpec.describe Mutant::Result::Mutation do
     )
   end
 
-  let(:mutation) do
-    instance_double(
-      Mutant::Mutation,
-      frozen?: true,
-      class:   class_double(Mutant::Mutation)
-    )
-  end
+  let(:mutation) { instance_double(Mutant::Mutation) }
 
   let(:test_result) do
     instance_double(
diff --git a/spec/unit/mutant/runner_spec.rb b/spec/unit/mutant/runner_spec.rb
index 8085dc93..5ac9a49b 100644
--- a/spec/unit/mutant/runner_spec.rb
+++ b/spec/unit/mutant/runner_spec.rb
@@ -1,6 +1,5 @@
 RSpec.describe Mutant::Runner do
   describe '.call' do
-    let(:integration) { instance_double(Mutant::Integration)            }
     let(:reporter)    { instance_double(Mutant::Reporter, delay: delay) }
     let(:driver)      { instance_double(Mutant::Parallel::Driver)       }
     let(:delay)       { instance_double(Float)                          }
@@ -21,10 +20,9 @@ RSpec.describe Mutant::Runner do
     let(:config) do
       instance_double(
         Mutant::Config,
-        integration: integration,
-        jobs:        1,
-        kernel:      kernel,
-        reporter:    reporter
+        jobs:     1,
+        kernel:   kernel,
+        reporter: reporter
       )
     end
 
diff --git a/spec/unit/mutant/subject_spec.rb b/spec/unit/mutant/subject_spec.rb
index c24aca36..92e85342 100644
--- a/spec/unit/mutant/subject_spec.rb
+++ b/spec/unit/mutant/subject_spec.rb
@@ -26,8 +26,7 @@ RSpec.describe Mutant::Subject do
   let(:context) do
     double(
       'Context',
-      source_path: 'source_path',
-      source_line: 'source_line'
+      source_path: 'source_path'
     )
   end