diff --git a/spec/spec_helper.rb b/spec/spec_helper.rb
index d5157948..e0abe295 100644
--- a/spec/spec_helper.rb
+++ b/spec/spec_helper.rb
@@ -59,7 +59,6 @@ end # MessageHelper
 
 RSpec.configure do |config|
   config.extend(SharedContext)
-  config.include(CompressHelper)
   config.include(MessageHelper)
   config.include(ParserHelper)
   config.include(Mutant::AST::Sexp)
diff --git a/spec/support/compress_helper.rb b/spec/support/compress_helper.rb
deleted file mode 100644
index 2f841bb3..00000000
--- a/spec/support/compress_helper.rb
+++ /dev/null
@@ -1,10 +0,0 @@
-# frozen_string_literal: true
-module CompressHelper
-  def strip_indent(string)
-    lines       = string.lines
-    match       = /\A( *)/.match(lines.first)
-    return string unless match
-    whitespaces = match[1].to_s.length
-    lines.map { |line| line[whitespaces..-1] }.join
-  end
-end # CompressHelper
diff --git a/spec/support/shared_context.rb b/spec/support/shared_context.rb
index df5f553f..9ac65022 100644
--- a/spec/support/shared_context.rb
+++ b/spec/support/shared_context.rb
@@ -28,7 +28,7 @@ module SharedContext
     it 'writes expected report to output' do
       described_class.call(output, reportable)
       output.rewind
-      expect(output.read).to eql(strip_indent(expected_content))
+      expect(output.read).to eql(expected_content)
     end
   end
 
diff --git a/spec/unit/mutant/cli_spec.rb b/spec/unit/mutant/cli_spec.rb
index e8f4e4f9..dd72e84e 100644
--- a/spec/unit/mutant/cli_spec.rb
+++ b/spec/unit/mutant/cli_spec.rb
@@ -108,21 +108,21 @@ RSpec.describe Mutant::CLI do
       it_should_behave_like 'a cli parser'
 
       let(:expected_message) do
-        strip_indent(<<-MESSAGE)
-usage: mutant [options] MATCH_EXPRESSION ...
-Environment:
-        --zombie                     Run mutant zombified
-    -I, --include DIRECTORY          Add DIRECTORY to $LOAD_PATH
-    -r, --require NAME               Require file with NAME
-    -j, --jobs NUMBER                Number of kill jobs. Defaults to number of processors.
+        <<~MESSAGE
+          usage: mutant [options] MATCH_EXPRESSION ...
+          Environment:
+                  --zombie                     Run mutant zombified
+              -I, --include DIRECTORY          Add DIRECTORY to $LOAD_PATH
+              -r, --require NAME               Require file with NAME
+              -j, --jobs NUMBER                Number of kill jobs. Defaults to number of processors.
 
-Options:
-        --use INTEGRATION            Use INTEGRATION to kill mutations
-        --ignore-subject EXPRESSION  Ignore subjects that match EXPRESSION as prefix
-        --since REVISION             Only select subjects touched since REVISION
-        --fail-fast                  Fail fast
-        --version                    Print mutants version
-    -h, --help                       Show this message
+          Options:
+                  --use INTEGRATION            Use INTEGRATION to kill mutations
+                  --ignore-subject EXPRESSION  Ignore subjects that match EXPRESSION as prefix
+                  --since REVISION             Only select subjects touched since REVISION
+                  --fail-fast                  Fail fast
+                  --version                    Print mutants version
+              -h, --help                       Show this message
         MESSAGE
       end
     end
diff --git a/spec/unit/mutant/diff_spec.rb b/spec/unit/mutant/diff_spec.rb
index b55b0c6f..5d0416fe 100644
--- a/spec/unit/mutant/diff_spec.rb
+++ b/spec/unit/mutant/diff_spec.rb
@@ -56,7 +56,7 @@ RSpec.describe Mutant::Diff do
       let(:new) { %w[baz bar baz] }
 
       let(:expectation) do
-        strip_indent(<<-STR)
+        <<~STR
           @@ -1,4 +1,4 @@
           -foo
           +baz
@@ -76,7 +76,7 @@ RSpec.describe Mutant::Diff do
       let(:new) { %w[baz bar] }
 
       let(:expectation) do
-        strip_indent(<<-STR)
+        <<~STR
           @@ -1,3 +1,3 @@
           -foo
           +baz
@@ -94,7 +94,7 @@ RSpec.describe Mutant::Diff do
       let(:new) { %w[foo baz bar] }
 
       let(:expectation) do
-        strip_indent(<<-STR)
+        <<~STR
           @@ -1,3 +1,4 @@
            foo
           +baz
@@ -112,7 +112,7 @@ RSpec.describe Mutant::Diff do
       let(:new) { %w[foo bar baz boz a b c other] }
 
       let(:expectation) do
-        strip_indent(<<-STR)
+        <<~STR
           @@ -1,8 +1,9 @@
            foo
            bar
@@ -135,7 +135,7 @@ RSpec.describe Mutant::Diff do
       let(:new) { %w[foo bar baz boz a b c]       }
 
       let(:expectation) do
-        strip_indent(<<-STR)
+        <<~STR
           @@ -1,9 +1,8 @@
           -other
            foo
@@ -158,7 +158,7 @@ RSpec.describe Mutant::Diff do
       let(:new) { %w[other foo bar baz boz a b c] }
 
       let(:expectation) do
-        strip_indent(<<-STR)
+        <<~STR
           @@ -1,8 +1,9 @@
           +other
            foo
diff --git a/spec/unit/mutant/meta/example/verification_spec.rb b/spec/unit/mutant/meta/example/verification_spec.rb
index 5470e922..99397bd7 100644
--- a/spec/unit/mutant/meta/example/verification_spec.rb
+++ b/spec/unit/mutant/meta/example/verification_spec.rb
@@ -63,7 +63,7 @@ RSpec.describe Mutant::Meta::Example::Verification do
       let(:expected_nodes) { [s(:false), s(:nil)] }
 
       specify do
-        should eql(strip_indent(<<-'REPORT'))
+        should eql(<<~'REPORT')
           ---
           file: foo.rb
           original_ast: s(:true)
@@ -83,7 +83,7 @@ RSpec.describe Mutant::Meta::Example::Verification do
       let(:generated_nodes) { [s(:false), s(:nil)] }
 
       specify do
-        should eql(strip_indent(<<-'REPORT'))
+        should eql(<<~'REPORT')
           ---
           file: foo.rb
           original_ast: s(:true)
@@ -104,7 +104,7 @@ RSpec.describe Mutant::Meta::Example::Verification do
       let(:generated_nodes) { [s(:true)] }
 
       specify do
-        should eql(strip_indent(<<-'REPORT'))
+        should eql(<<~'REPORT')
           ---
           file: foo.rb
           original_ast: s(:true)
diff --git a/spec/unit/mutant/reporter/cli/printer/config_spec.rb b/spec/unit/mutant/reporter/cli/printer/config_spec.rb
index 76b7340d..c7ffe231 100644
--- a/spec/unit/mutant/reporter/cli/printer/config_spec.rb
+++ b/spec/unit/mutant/reporter/cli/printer/config_spec.rb
@@ -6,7 +6,7 @@ RSpec.describe Mutant::Reporter::CLI::Printer::Config do
 
   describe '.call' do
     context 'on default config' do
-      it_reports(<<-REPORT)
+      it_reports(<<~REPORT)
         Mutant configuration:
         Matcher:         #<Mutant::Matcher::Config empty>
         Integration:     Mutant::Integration::Null
@@ -17,7 +17,7 @@ RSpec.describe Mutant::Reporter::CLI::Printer::Config do
     end
 
     context 'with non default coverage expectation' do
-      it_reports(<<-REPORT)
+      it_reports(<<~REPORT)
         Mutant configuration:
         Matcher:         #<Mutant::Matcher::Config empty>
         Integration:     Mutant::Integration::Null
diff --git a/spec/unit/mutant/reporter/cli/printer/env_progress_spec.rb b/spec/unit/mutant/reporter/cli/printer/env_progress_spec.rb
index 6cd0bd1a..f3d00f61 100644
--- a/spec/unit/mutant/reporter/cli/printer/env_progress_spec.rb
+++ b/spec/unit/mutant/reporter/cli/printer/env_progress_spec.rb
@@ -8,7 +8,7 @@ RSpec.describe Mutant::Reporter::CLI::Printer::EnvProgress do
     context 'without progress' do
       with(:subject_a_result) { { mutation_results: [] } }
 
-      it_reports <<-'STR'
+      it_reports <<~'STR'
         Mutant configuration:
         Matcher:         #<Mutant::Matcher::Config empty>
         Integration:     Mutant::Integration::Null
@@ -29,7 +29,7 @@ RSpec.describe Mutant::Reporter::CLI::Printer::EnvProgress do
     end
 
     context 'on full coverage' do
-      it_reports <<-'STR'
+      it_reports <<~'STR'
         Mutant configuration:
         Matcher:         #<Mutant::Matcher::Config empty>
         Integration:     Mutant::Integration::Null
@@ -52,7 +52,7 @@ RSpec.describe Mutant::Reporter::CLI::Printer::EnvProgress do
     context 'on partial coverage' do
       with(:mutation_a_test_result) { { passed: true } }
 
-      it_reports <<-'STR'
+      it_reports <<~'STR'
         Mutant configuration:
         Matcher:         #<Mutant::Matcher::Config empty>
         Integration:     Mutant::Integration::Null
diff --git a/spec/unit/mutant/reporter/cli/printer/env_result_spec.rb b/spec/unit/mutant/reporter/cli/printer/env_result_spec.rb
index 2f951053..775c06e8 100644
--- a/spec/unit/mutant/reporter/cli/printer/env_result_spec.rb
+++ b/spec/unit/mutant/reporter/cli/printer/env_result_spec.rb
@@ -7,7 +7,7 @@ RSpec.describe Mutant::Reporter::CLI::Printer::EnvResult do
   let(:reportable) { env_result }
 
   describe '.call' do
-    it_reports <<-'STR'
+    it_reports <<~'STR'
       subject-a
       - test-a
       evil:subject-a:d27d2
diff --git a/spec/unit/mutant/reporter/cli/printer/mutation_result_spec.rb b/spec/unit/mutant/reporter/cli/printer/mutation_result_spec.rb
index a256bc67..b8f808b6 100644
--- a/spec/unit/mutant/reporter/cli/printer/mutation_result_spec.rb
+++ b/spec/unit/mutant/reporter/cli/printer/mutation_result_spec.rb
@@ -27,7 +27,7 @@ RSpec.describe Mutant::Reporter::CLI::Printer::MutationResult do
           end
 
           context 'on non tty' do
-            it_reports(<<-'STR')
+            it_reports(<<~'STR')
               evil:subject-a:d27d2
               @@ -1,2 +1,2 @@
               -true
@@ -44,7 +44,7 @@ RSpec.describe Mutant::Reporter::CLI::Printer::MutationResult do
           # Unparses exactly the same way as above node
           let(:mutation_a_node) { s(:zsuper) }
 
-          it_reports(<<-REPORT)
+          it_reports(<<~REPORT)
             evil:subject-a:a5bc7
             --- Internal failure ---
             BUG: Mutation NOT resulted in exactly one diff hunk. Please report a reproduction!
@@ -68,7 +68,7 @@ RSpec.describe Mutant::Reporter::CLI::Printer::MutationResult do
           Mutant::Mutation::Neutral.new(subject_a, s(:true))
         end
 
-        it_reports(<<-REPORT)
+        it_reports(<<~REPORT)
           neutral:subject-a:d5318
           --- Neutral failure ---
           Original code was inserted unmutated. And the test did NOT PASS.
@@ -93,7 +93,7 @@ RSpec.describe Mutant::Reporter::CLI::Printer::MutationResult do
           Mutant::Mutation::Noop.new(subject_a, s(:true))
         end
 
-        it_reports(<<-REPORT)
+        it_reports(<<~REPORT)
           noop:subject-a:d5318
           ---- Noop failure -----
           No code was inserted. And the test did NOT PASS.
diff --git a/spec/unit/mutant/reporter/cli/printer/status_progressive_spec.rb b/spec/unit/mutant/reporter/cli/printer/status_progressive_spec.rb
index 684117fd..90bb87cf 100644
--- a/spec/unit/mutant/reporter/cli/printer/status_progressive_spec.rb
+++ b/spec/unit/mutant/reporter/cli/printer/status_progressive_spec.rb
@@ -8,7 +8,7 @@ RSpec.describe Mutant::Reporter::CLI::Printer::StatusProgressive do
     context 'with empty scheduler' do
       with(:env_result) { { subject_results: [] } }
 
-      it_reports <<-REPORT
+      it_reports <<~REPORT
         (00/02) 100% - killtime: 0.00s runtime: 4.00s overhead: 4.00s
       REPORT
     end
@@ -17,7 +17,7 @@ RSpec.describe Mutant::Reporter::CLI::Printer::StatusProgressive do
       context 'without progress' do
         with(:status) { { active_jobs: [].to_set } }
 
-        it_reports(<<-REPORT)
+        it_reports(<<~REPORT)
           (02/02) 100% - killtime: 2.00s runtime: 4.00s overhead: 2.00s
         REPORT
       end
@@ -28,13 +28,13 @@ RSpec.describe Mutant::Reporter::CLI::Printer::StatusProgressive do
         context 'on failure' do
           with(:mutation_a_test_result) { { passed: true } }
 
-          it_reports(<<-REPORT)
+          it_reports(<<~REPORT)
             (01/02)  50% - killtime: 2.00s runtime: 4.00s overhead: 2.00s
           REPORT
         end
 
         context 'on success' do
-          it_reports(<<-REPORT)
+          it_reports(<<~REPORT)
             (02/02) 100% - killtime: 2.00s runtime: 4.00s overhead: 2.00s
           REPORT
         end
diff --git a/spec/unit/mutant/reporter/cli/printer/status_spec.rb b/spec/unit/mutant/reporter/cli/printer/status_spec.rb
index 8f503f4e..69a8fd39 100644
--- a/spec/unit/mutant/reporter/cli/printer/status_spec.rb
+++ b/spec/unit/mutant/reporter/cli/printer/status_spec.rb
@@ -8,7 +8,7 @@ RSpec.describe Mutant::Reporter::CLI::Printer::Status do
     context 'with empty scheduler' do
       with(:env_result) { { subject_results: [] } }
 
-      it_reports <<-REPORT
+      it_reports <<~REPORT
         Mutant configuration:
         Matcher:         #<Mutant::Matcher::Config empty>
         Integration:     Mutant::Integration::Null
@@ -33,7 +33,7 @@ RSpec.describe Mutant::Reporter::CLI::Printer::Status do
       context 'without progress' do
         with(:status) { { active_jobs: [].to_set } }
 
-        it_reports(<<-REPORT)
+        it_reports(<<~REPORT)
           Mutant configuration:
           Matcher:         #<Mutant::Matcher::Config empty>
           Integration:     Mutant::Integration::Null
@@ -60,7 +60,7 @@ RSpec.describe Mutant::Reporter::CLI::Printer::Status do
         context 'on failure' do
           with(:mutation_a_test_result) { { passed: true } }
 
-          it_reports(<<-REPORT)
+          it_reports(<<~REPORT)
             Mutant configuration:
             Matcher:         #<Mutant::Matcher::Config empty>
             Integration:     Mutant::Integration::Null
@@ -88,7 +88,7 @@ RSpec.describe Mutant::Reporter::CLI::Printer::Status do
         end
 
         context 'on success' do
-          it_reports(<<-REPORT)
+          it_reports(<<~REPORT)
             Mutant configuration:
             Matcher:         #<Mutant::Matcher::Config empty>
             Integration:     Mutant::Integration::Null
diff --git a/spec/unit/mutant/reporter/cli/printer/subject_progress_spec.rb b/spec/unit/mutant/reporter/cli/printer/subject_progress_spec.rb
index a525879a..38946446 100644
--- a/spec/unit/mutant/reporter/cli/printer/subject_progress_spec.rb
+++ b/spec/unit/mutant/reporter/cli/printer/subject_progress_spec.rb
@@ -6,7 +6,7 @@ RSpec.describe Mutant::Reporter::CLI::Printer::SubjectProgress do
 
   describe '.call' do
     context 'on full coverage' do
-      it_reports <<-'STR'
+      it_reports <<~'STR'
         subject-a mutations: 2
         ..
         (02/02) 100% - killtime: 2.00s runtime: 2.00s overhead: 0.00s
@@ -16,7 +16,7 @@ RSpec.describe Mutant::Reporter::CLI::Printer::SubjectProgress do
     context 'on partial coverage' do
       with(:mutation_a_test_result) { { passed: true } }
 
-      it_reports <<-'STR'
+      it_reports <<~'STR'
         subject-a mutations: 2
         F.
         (01/02)  50% - killtime: 2.00s runtime: 2.00s overhead: 0.00s
@@ -26,7 +26,7 @@ RSpec.describe Mutant::Reporter::CLI::Printer::SubjectProgress do
     context 'without results' do
       with(:subject_a_result) { { mutation_results: [] } }
 
-      it_reports <<-'STR'
+      it_reports <<~'STR'
         subject-a mutations: 2
         (00/02) 100% - killtime: 0.00s runtime: 0.00s overhead: 0.00s
       STR
diff --git a/spec/unit/mutant/reporter/cli/printer/subject_result_spec.rb b/spec/unit/mutant/reporter/cli/printer/subject_result_spec.rb
index ae5e3aa8..a6ce289f 100644
--- a/spec/unit/mutant/reporter/cli/printer/subject_result_spec.rb
+++ b/spec/unit/mutant/reporter/cli/printer/subject_result_spec.rb
@@ -6,7 +6,7 @@ RSpec.describe Mutant::Reporter::CLI::Printer::SubjectResult do
 
   describe '.call' do
     context 'on full coverage' do
-      it_reports <<-'STR'
+      it_reports <<~'STR'
         subject-a
         - test-a
       STR
@@ -15,7 +15,7 @@ RSpec.describe Mutant::Reporter::CLI::Printer::SubjectResult do
     context 'on partial coverage' do
       with(:mutation_a_test_result) { { passed: true } }
 
-      it_reports <<-'STR'
+      it_reports <<~'STR'
         subject-a
         - test-a
         evil:subject-a:d27d2
@@ -29,7 +29,7 @@ RSpec.describe Mutant::Reporter::CLI::Printer::SubjectResult do
     context 'without results' do
       with(:subject_a_result) { { mutation_results: [] } }
 
-      it_reports <<-'STR'
+      it_reports <<~'STR'
         subject-a
         - test-a
       STR
diff --git a/spec/unit/mutant/reporter/cli/printer/test_result_spec.rb b/spec/unit/mutant/reporter/cli/printer/test_result_spec.rb
index b06a23e6..a0bbaa0e 100644
--- a/spec/unit/mutant/reporter/cli/printer/test_result_spec.rb
+++ b/spec/unit/mutant/reporter/cli/printer/test_result_spec.rb
@@ -5,7 +5,7 @@ RSpec.describe Mutant::Reporter::CLI::Printer::TestResult do
   let(:reportable) { mutation_a_test_result }
 
   describe '.call' do
-    it_reports <<-'STR'
+    it_reports <<~'STR'
       - 1 @ runtime: 1.0
         - test-a
       Test Output:
diff --git a/spec/unit/mutant/reporter/cli/printer_spec.rb b/spec/unit/mutant/reporter/cli/printer_spec.rb
index 825e7c81..2232c7e6 100644
--- a/spec/unit/mutant/reporter/cli/printer_spec.rb
+++ b/spec/unit/mutant/reporter/cli/printer_spec.rb
@@ -9,7 +9,7 @@ RSpec.describe Mutant::Reporter::CLI::Printer do
       allow(output).to receive(:tty?).and_return(tty?)
       subject
       output.rewind
-      expect(output.read).to eql(strip_indent(expectation))
+      expect(output.read).to eql(expectation)
     end
   end
 
diff --git a/spec/unit/mutant/reporter/cli_spec.rb b/spec/unit/mutant/reporter/cli_spec.rb
index aae8e874..53c1153f 100644
--- a/spec/unit/mutant/reporter/cli_spec.rb
+++ b/spec/unit/mutant/reporter/cli_spec.rb
@@ -35,7 +35,7 @@ RSpec.describe Mutant::Reporter::CLI do
   def self.it_reports(expected_content)
     it 'writes expected report to output' do
       expect(subject).to be(object)
-      expect(contents).to eql(strip_indent(expected_content))
+      expect(contents).to eql(expected_content)
     end
   end
 
@@ -119,7 +119,7 @@ RSpec.describe Mutant::Reporter::CLI do
     context 'on progressive format' do
       let(:format) { progressive_format }
 
-      it_reports(<<-REPORT)
+      it_reports(<<~REPORT)
         Mutant configuration:
         Matcher:         #<Mutant::Matcher::Config empty>
         Integration:     Mutant::Integration::Null
@@ -137,7 +137,7 @@ RSpec.describe Mutant::Reporter::CLI do
   describe '#report' do
     subject { object.report(env_result) }
 
-    it_reports(<<-REPORT)
+    it_reports(<<~REPORT)
       Mutant configuration:
       Matcher:         #<Mutant::Matcher::Config empty>
       Integration:     Mutant::Integration::Null
@@ -163,7 +163,7 @@ RSpec.describe Mutant::Reporter::CLI do
     context 'on framed format' do
       let(:format) { framed_format }
 
-      it_reports(<<-REPORT)
+      it_reports(<<~REPORT)
         [tput-restore]Mutant configuration:
         Matcher:         #<Mutant::Matcher::Config empty>
         Integration:     Mutant::Integration::Null