Add DisabledFormatter to trace disabled lines

spec/ameba/formatter/disabled_formatter_spec.cr

@@ -0,0 +1,41 @@
+require "../../spec_helper"
+
+module Ameba::Formatter
+  describe DisabledFormatter do
+    output = IO::Memory.new
+    subject = DisabledFormatter.new output
+
+    describe "#finished" do
+      it "writes a final message" do
+        subject.finished [Source.new ""]
+        output.to_s.should contain "Disabled rules using inline directives:"
+      end
+
+      it "writes disabled rules if any" do
+        Colorize.enabled = false
+
+        path = "source.cr"
+        s = Source.new("", path).tap do |s|
+          s.error(ErrorRule.new, 1, 2, "ErrorRule", :disabled)
+          s.error(NamedRule.new, 2, 2, "NamedRule", :disabled)
+        end
+        subject.finished [s]
+        log = output.to_s
+        log.should contain "#{path}:1 #{ErrorRule.name}"
+        log.should contain "#{path}:2 #{NamedRule.name}"
+      ensure
+        output.clear
+        Colorize.enabled = true
+      end
+
+      it "does not write not-disabled rules" do
+        s = Source.new("", "source.cr").tap do |s|
+          s.error(ErrorRule.new, 1, 2, "ErrorRule")
+          s.error(NamedRule.new, 2, 2, "NamedRule", :disabled)
+        end
+        subject.finished [s]
+        output.to_s.should_not contain ErrorRule.name
+      end
+    end
+  end
+end