diff --git a/spec/ameba/rule_spec.cr b/spec/ameba/rule_spec.cr
index 91513784..cc86580a 100644
--- a/spec/ameba/rule_spec.cr
+++ b/spec/ameba/rule_spec.cr
@@ -11,7 +11,7 @@ module Ameba
 
     describe "#name" do
       it "returns name of the rule" do
-        DummyRule.new.name.should eq "DummyRule"
+        DummyRule.new.name.should eq "Ameba::DummyRule"
       end
     end
 
diff --git a/spec/ameba/rules/comparison_to_boolean_spec.cr b/spec/ameba/rules/comparison_to_boolean_spec.cr
index 0e068930..34d938dd 100644
--- a/spec/ameba/rules/comparison_to_boolean_spec.cr
+++ b/spec/ameba/rules/comparison_to_boolean_spec.cr
@@ -33,7 +33,7 @@ module Ameba::Rules
           :not_ok
         end
       )
-      subject.catch(source).valid?.should be_true
+      subject.catch(source).should be_valid
     end
 
     context "boolean on the right" do
@@ -43,7 +43,7 @@ module Ameba::Rules
             :ok
           end
         )
-        subject.catch(source).valid?.should be_false
+        subject.catch(source).should_not be_valid
       end
 
       it "fails if there is != comparison to boolean" do
@@ -52,14 +52,14 @@ module Ameba::Rules
             :ok
           end
         )
-        subject.catch(source).valid?.should be_false
+        subject.catch(source).should_not be_valid
       end
 
       it "fails if there is case comparison to boolean" do
         source = Source.new %(
           a === true
         )
-        subject.catch(source).valid?.should be_false
+        subject.catch(source).should_not be_valid
       end
 
       it "reports rule, pos and message" do
@@ -80,7 +80,7 @@ module Ameba::Rules
             :ok
           end
         )
-        subject.catch(source).valid?.should be_false
+        subject.catch(source).should_not be_valid
       end
 
       it "fails if there is != comparison to boolean" do
@@ -89,19 +89,19 @@ module Ameba::Rules
             :ok
           end
         )
-        subject.catch(source).valid?.should be_false
+        subject.catch(source).should_not be_valid
       end
 
       it "fails if there is case comparison to boolean" do
         source = Source.new %(
           true === a
         )
-        subject.catch(source).valid?.should be_false
+        subject.catch(source).should_not be_valid
       end
 
       it "reports rule, pos and message" do
         source = Source.new "true != a"
-        subject.catch(source)
+        subject.catch(source).should_not be_valid
 
         error = source.errors.first
         error.rule.should_not be_nil
diff --git a/spec/ameba/rules/debugger_statement_spec.cr b/spec/ameba/rules/debugger_statement_spec.cr
index 85e8b132..2b14f7ac 100644
--- a/spec/ameba/rules/debugger_statement_spec.cr
+++ b/spec/ameba/rules/debugger_statement_spec.cr
@@ -19,7 +19,7 @@ module Ameba::Rules
         end
         A.new.debugger
       )
-      subject.catch(s).valid?.should be_true
+      subject.catch(s).should be_valid
     end
 
     it "fails if there is a debugger statement" do
@@ -28,12 +28,12 @@ module Ameba::Rules
         debugger
         a = a + 1
       )
-      subject.catch(s).valid?.should be_false
+      subject.catch(s).should_not be_valid
     end
 
     it "reports rule, pos and message" do
       s = Source.new "debugger"
-      subject.catch(s).valid?.should be_false
+      subject.catch(s).should_not be_valid
 
       error = s.errors.first
       error.rule.should_not be_nil
diff --git a/spec/ameba/rules/line_length_spec.cr b/spec/ameba/rules/line_length_spec.cr
index 23b25098..b34bde5c 100644
--- a/spec/ameba/rules/line_length_spec.cr
+++ b/spec/ameba/rules/line_length_spec.cr
@@ -7,22 +7,22 @@ module Ameba::Rules
   describe LineLength do
     it "passes if all lines are shorter than 80 symbols" do
       source = Source.new "short line"
-      subject.catch(source).valid?.should be_true
+      subject.catch(source).should be_valid
     end
 
     it "passes if line consists of 79 symbols" do
       source = Source.new "*" * 79
-      subject.catch(source).valid?.should be_true
+      subject.catch(source).should be_valid
     end
 
     it "fails if there is at least one line longer than 79 symbols" do
       source = Source.new long_line
-      subject.catch(source).valid?.should be_false
+      subject.catch(source).should_not be_valid
     end
 
     it "reports rule, pos and message" do
       source = Source.new long_line
-      subject.catch(source).valid?.should be_false
+      subject.catch(source).should_not be_valid
 
       error = source.errors.first
       error.rule.should eq subject
diff --git a/spec/ameba/rules/literal_in_condition_spec.cr b/spec/ameba/rules/literal_in_condition_spec.cr
index a8fb0e09..c993fcb5 100644
--- a/spec/ameba/rules/literal_in_condition_spec.cr
+++ b/spec/ameba/rules/literal_in_condition_spec.cr
@@ -23,7 +23,7 @@ module Ameba::Rules
           :ok
         end
       )
-      subject.catch(s).valid?.should be_true
+      subject.catch(s).should be_valid
     end
 
     it "fails if there is a predicate in if conditional" do
@@ -32,7 +32,7 @@ module Ameba::Rules
           :ok
         end
       )
-      subject.catch(s).valid?.should be_false
+      subject.catch(s).should_not be_valid
     end
 
     it "fails if there is a predicate in unless conditional" do
@@ -41,7 +41,7 @@ module Ameba::Rules
           :ok
         end
       )
-      subject.catch(s).valid?.should be_false
+      subject.catch(s).should_not be_valid
     end
 
     it "fails if there is a predicate in case conditional" do
@@ -53,14 +53,14 @@ module Ameba::Rules
           :also_ok
         end
       )
-      subject.catch(s).valid?.should be_false
+      subject.catch(s).should_not be_valid
     end
 
     it "reports rule, pos and message" do
       s = Source.new %(
         puts "hello" if true
       )
-      subject.catch(s)
+      subject.catch(s).should_not be_valid
 
       s.errors.size.should eq 1
       error = s.errors.first
diff --git a/spec/ameba/rules/literal_in_interpolation_spec.cr b/spec/ameba/rules/literal_in_interpolation_spec.cr
index 2977845e..1438ec42 100644
--- a/spec/ameba/rules/literal_in_interpolation_spec.cr
+++ b/spec/ameba/rules/literal_in_interpolation_spec.cr
@@ -13,7 +13,7 @@ module Ameba::Rules
 
         "Name size: #{name.size}"
       )
-      subject.catch(s).valid?.should be_true
+      subject.catch(s).should be_valid
     end
 
     it "fails if there is useless interpolation" do
@@ -24,13 +24,13 @@ module Ameba::Rules
         %q("#{false}"),
         %q("here are #{4} cats"),
       ].each do |str|
-        subject.catch(Source.new str).valid?.should be_false
+        subject.catch(Source.new str).should_not be_valid
       end
     end
 
     it "reports rule, pos and message" do
       s = Source.new %q("#{4}")
-      subject.catch(s).valid?.should be_false
+      subject.catch(s).should_not be_valid
 
       error = s.errors.first
       error.rule.should_not be_nil
diff --git a/spec/ameba/rules/negated_conditions_in_unless_spec.cr b/spec/ameba/rules/negated_conditions_in_unless_spec.cr
index 5c29ae49..4ea3474c 100644
--- a/spec/ameba/rules/negated_conditions_in_unless_spec.cr
+++ b/spec/ameba/rules/negated_conditions_in_unless_spec.cr
@@ -16,7 +16,7 @@ module Ameba::Rules
           :ok
         end
       )
-      subject.catch(s).valid?.should be_true
+      subject.catch(s).should be_valid
     end
 
     it "fails if there is a negated condition in unless" do
@@ -25,7 +25,7 @@ module Ameba::Rules
           :nok
         end
       )
-      subject.catch(s).valid?.should be_false
+      subject.catch(s).should_not be_valid
     end
 
     it "fails if one of AND conditions is negated" do
@@ -34,7 +34,7 @@ module Ameba::Rules
           :nok
         end
       )
-      subject.catch(s).valid?.should be_false
+      subject.catch(s).should_not be_valid
     end
 
     it "fails if one of OR conditions is negated" do
@@ -43,7 +43,7 @@ module Ameba::Rules
           :nok
         end
       )
-      subject.catch(s).valid?.should be_false
+      subject.catch(s).should_not be_valid
     end
 
     it "fails if one of inner conditions is negated" do
@@ -52,12 +52,12 @@ module Ameba::Rules
           :nok
         end
       )
-      subject.catch(s).valid?.should be_false
+      subject.catch(s).should_not be_valid
     end
 
     it "reports rule, pos and message" do
       s = Source.new ":nok unless !s.empty?"
-      subject.catch(s).valid?.should be_false
+      subject.catch(s).should_not be_valid
 
       error = s.errors.first
       error.rule.should_not be_nil
diff --git a/spec/ameba/rules/predicate_name_spec.cr b/spec/ameba/rules/predicate_name_spec.cr
index 7e7ab3c6..70902a20 100644
--- a/spec/ameba/rules/predicate_name_spec.cr
+++ b/spec/ameba/rules/predicate_name_spec.cr
@@ -14,7 +14,7 @@ module Ameba::Rules
           end
         end
       )
-      subject.catch(s).valid?.should be_true
+      subject.catch(s).should be_valid
     end
 
     it "fails if predicate name is wrong" do
@@ -22,7 +22,7 @@ module Ameba::Rules
         def is_valid?(x)
         end
       )
-      subject.catch(s).valid?.should be_false
+      subject.catch(s).should_not be_valid
     end
 
     it "reports rule, pos and message" do
@@ -33,7 +33,7 @@ module Ameba::Rules
           end
         end
       )
-      subject.catch(s).valid?.should be_false
+      subject.catch(s).should_not be_valid
 
       error = s.errors.first
       error.rule.should_not be_nil
diff --git a/spec/ameba/rules/trailing_blank_lines_spec.cr b/spec/ameba/rules/trailing_blank_lines_spec.cr
index 1c7e5572..abb1ef16 100644
--- a/spec/ameba/rules/trailing_blank_lines_spec.cr
+++ b/spec/ameba/rules/trailing_blank_lines_spec.cr
@@ -6,27 +6,27 @@ module Ameba::Rules
   describe TrailingBlankLines do
     it "passes if there is no blank lines at the end" do
       source = Source.new "no-blankline"
-      subject.catch(source).valid?.should be_true
+      subject.catch(source).should be_valid
     end
 
     it "fails if there is a blank line at the end of a source" do
       source = Source.new "a = 1\n \n "
-      subject.catch(source).valid?.should be_false
+      subject.catch(source).should_not be_valid
     end
 
     it "passes if source is empty" do
       source = Source.new ""
-      subject.catch(source).valid?.should be_true
+      subject.catch(source).should be_valid
     end
 
     it "passes if last line is not blank" do
       source = Source.new "\n\n\n puts 22"
-      subject.catch(source).valid?.should be_true
+      subject.catch(source).should be_valid
     end
 
     it "reports rule, pos and message" do
       source = Source.new "a = 1\n\n "
-      subject.catch(source)
+      subject.catch(source).should_not be_valid
 
       error = source.errors.first
       error.rule.should_not be_nil
diff --git a/spec/ameba/rules/trailing_whitespace_spec.cr b/spec/ameba/rules/trailing_whitespace_spec.cr
index c88d0868..2bebc298 100644
--- a/spec/ameba/rules/trailing_whitespace_spec.cr
+++ b/spec/ameba/rules/trailing_whitespace_spec.cr
@@ -6,17 +6,17 @@ module Ameba::Rules
   describe TrailingWhitespace do
     it "passes if all lines do not have trailing whitespace" do
       source = Source.new "no-whispace"
-      subject.catch(source).valid?.should be_true
+      subject.catch(source).should be_valid
     end
 
     it "fails if there is a line with trailing whitespace" do
       source = Source.new "whitespace at the end "
-      subject.catch(source).valid?.should be_false
+      subject.catch(source).should_not be_valid
     end
 
     it "reports rule, pos and message" do
       source = Source.new "a = 1\n b = 2 "
-      subject.catch(source).valid?.should be_false
+      subject.catch(source).should_not be_valid
 
       error = source.errors.first
       error.rule.should_not be_nil
diff --git a/spec/ameba/rules/unless_else_spec.cr b/spec/ameba/rules/unless_else_spec.cr
index ebd40066..0dead8e2 100644
--- a/spec/ameba/rules/unless_else_spec.cr
+++ b/spec/ameba/rules/unless_else_spec.cr
@@ -10,7 +10,7 @@ module Ameba::Rules
           :ok
         end
       )
-      subject.catch(s).valid?.should be_true
+      subject.catch(s).should be_valid
     end
 
     it "fails if unless has else" do
@@ -21,7 +21,7 @@ module Ameba::Rules
           :two
         end
       )
-      subject.catch(s).valid?.should be_false
+      subject.catch(s).should_not be_valid
     end
 
     it "reports rule, pos and message" do
@@ -32,7 +32,7 @@ module Ameba::Rules
           :two
         end
       )
-      subject.catch(s)
+      subject.catch(s).should_not be_valid
 
       error = s.errors.first
       error.should_not be_nil
diff --git a/spec/spec_helper.cr b/spec/spec_helper.cr
index 519c1729..19b5e278 100644
--- a/spec/spec_helper.cr
+++ b/spec/spec_helper.cr
@@ -1,7 +1,32 @@
 require "spec"
 require "../src/ameba"
 
-struct DummyRule < Ameba::Rule
-  def test(source)
+module Ameba
+  struct DummyRule < Ameba::Rule
+    def test(source)
+    end
+  end
+
+  struct BeValidExpectation
+    def match(source)
+      source.valid?
+    end
+
+    def failure_message(source)
+      String.build do |str|
+        str << "Source expected to be valid, but there are errors:\n\n"
+        source.errors.each do |e|
+          str << "  * #{e.rule.name}:#{e.pos} #{e.message}\n"
+        end
+      end
+    end
+
+    def negative_failure_message(source)
+      "Source expected to be invalid, but it is valid."
+    end
   end
 end
+
+def be_valid
+  Ameba::BeValidExpectation.new
+end