Add warning expectation class

config/flay.yml

@@ -1,3 +1,3 @@
 ---
 threshold: 18
-total_score: 822
+total_score: 836

lib/mutant.rb

@@ -81,6 +81,7 @@ require 'mutant/version'
 require 'mutant/cache'
 require 'mutant/node_helpers'
 require 'mutant/warning_filter'
+require 'mutant/warning_expectation'
 require 'mutant/constants'
 require 'mutant/random'
 require 'mutant/walker'

lib/mutant/warning_expectation.rb

@@ -0,0 +1,40 @@
+module Mutant
+  # A class to expect some warning message raising on absence of unexpected warnings
+  class WarningExpectation
+    include Adamantium::Flat, Concord.new(:expected)
+
+    # Error raised on expectation miss
+    class ExpectationError < RuntimeError
+      include Concord.new(:unexpected, :missing)
+
+      # Return exception message
+      #
+      # @return [String]
+      #
+      # @api private
+      #
+      def message
+        "Unexpected warnings: #{unexpected.inspect} missing warnigns: #{missing.inspect}"
+      end
+    end
+
+    # Execute blocks with warning expectations
+    #
+    # @return [self]
+    #
+    # @api private
+    #
+    def execute(&block)
+      warnings = WarningFilter.use do
+        block.call
+      end
+      missing = expected - warnings
+      unexpected = warnings - expected
+      if missing.any? or unexpected.any?
+        fail ExpectationError.new(unexpected, missing)
+      end
+      self
+    end
+
+  end # WarningExpectation
+end # Mutant

spec/unit/mutant/warning_expectation.rb

@@ -0,0 +1,71 @@
+require 'spec_helper'
+
+describe Mutant::WarningExpectation do
+  let(:object) { described_class.new(expected_warnings) }
+
+  let(:expected_warnings) { [] }
+  let(:warnings) { [] }
+
+  let(:warning_a) { "foo.rb:10: warning: We have a problem!\n" }
+  let(:warning_b) { "bar.rb:10: warning: We have an other problem!\n" }
+
+  describe '#execute' do
+    subject { object.execute(&block) }
+
+    before do
+      @called = false
+    end
+
+    let(:block) do
+      lambda do
+        @called = true
+        warnings.each(&Kernel.method(:warn))
+      end
+    end
+
+    it 'executes block' do
+      expect { subject }.to change { @called }.from(false).to(true)
+    end
+
+    context 'when no warnings occur during block execution' do
+      context 'and no warnings are expected' do
+        it_should_behave_like 'a command method'
+      end
+
+      context 'and warnings are expected' do
+        let(:expected_warnings) { [warning_a] }
+
+        it 'raises an expectation error' do
+          expect { subject }.to raise_error(Mutant::WarningExpectation::ExpectationError.new([], [warning_a]))
+        end
+      end
+    end
+
+    context 'when warnings occur during block execution' do
+      let(:warnings) { [warning_a, warning_b] }
+
+      context 'and only some no warnings are expected' do
+        let(:expected_warnings) { [warning_a] }
+
+        it 'raises an expectation error' do
+          expect { subject }.to raise_error(Mutant::WarningExpectation::ExpectationError.new([warning_b], []))
+        end
+      end
+
+      context 'and all warnings are expected' do
+        let(:expected_warnings) { [warning_a, warning_b] }
+
+        it_should_behave_like 'a command method'
+      end
+
+      context 'and there is an expected warning missing' do
+        let(:expected_warnings) { [warning_a] }
+        let(:warnings)          { [warning_b] }
+
+        it 'raises an expectation error' do
+          expect { subject }.to raise_error(Mutant::WarningExpectation::ExpectationError.new([warning_b], [warning_a]))
+        end
+      end
+    end
+  end
+end