Add flycheck formatter

refs #26

spec/ameba/formatter/flycheck_formatter_spec.cr

@@ -0,0 +1,44 @@
+require "../../spec_helper"
+
+private def flycheck
+  output = IO::Memory.new
+  Ameba::Formatter::FlycheckFormatter.new output
+end
+
+module Ameba::Formatter
+  describe FlycheckFormatter do
+    context "problems not found" do
+      it "reports nothing" do
+        subject = flycheck
+        subject.source_finished Source.new ""
+        subject.output.to_s.empty?.should be_true
+      end
+    end
+
+    context "when problems found" do
+      it "reports an error" do
+        s = Source.new "a = 1", "source.cr"
+        s.error DummyRule.new, s.location(1, 2), "message"
+        subject = flycheck
+        subject.source_finished s
+        subject.output.to_s.should eq "source.cr:1:2: E: message\n"
+      end
+
+      it "properly reports multi-line message" do
+        s = Source.new "a = 1", "source.cr"
+        s.error DummyRule.new, s.location(1, 2), "multi\nline"
+        subject = flycheck
+        subject.source_finished s
+        subject.output.to_s.should eq "source.cr:1:2: E: multi line\n"
+      end
+
+      it "reports nothing if location was not set" do
+        s = Source.new "a = 1", "source.cr"
+        s.error DummyRule.new, nil, "message"
+        subject = flycheck
+        subject.source_finished s
+        subject.output.to_s.should eq ""
+      end
+    end
+  end
+end