Major rework of codebase

- Get rid of 'core' and move CLI to cmd/gas directory
- Migrate (most) tests to use Ginkgo and testutils framework
- GAS now expects package to reside in $GOPATH
- GAS now can resolve dependencies for better type checking (if package
  on GOPATH)
- Simplified public API

rules/rules_test.go

@@ -0,0 +1,67 @@
+package rules_test
+
+import (
+	"bytes"
+	"fmt"
+	"log"
+
+	"github.com/GoASTScanner/gas"
+
+	"github.com/GoASTScanner/gas/rules"
+	"github.com/GoASTScanner/gas/testutils"
+	. "github.com/onsi/ginkgo"
+	. "github.com/onsi/gomega"
+)
+
+var _ = Describe("gas rules", func() {
+
+	var (
+		logger   *log.Logger
+		output   *bytes.Buffer
+		config   gas.Config
+		analyzer *gas.Analyzer
+		runner   func(string, []testutils.CodeSample)
+	)
+
+	BeforeEach(func() {
+		logger, output = testutils.NewLogger()
+		config = gas.NewConfig()
+		analyzer = gas.NewAnalyzer(config, logger)
+		runner = func(rule string, samples []testutils.CodeSample) {
+			analyzer.LoadRules(rules.Generate(rules.NewRuleFilter(false, rule)).Builders()...)
+			for n, sample := range samples {
+				analyzer.Reset()
+				pkg := testutils.NewTestPackage()
+				pkg.AddFile(fmt.Sprintf("sample_%d.go", n), sample.Code)
+				pkg.Build()
+				e := analyzer.Process(pkg.Path)
+				Expect(e).ShouldNot(HaveOccurred())
+				issues, _ := analyzer.Report()
+				if len(issues) != sample.Errors {
+					fmt.Println(sample.Code)
+				}
+				Expect(issues).Should(HaveLen(sample.Errors))
+			}
+		}
+	})
+
+	Context("report correct errors for all samples", func() {
+		It("should work for G101 samples", func() {
+			runner("G101", testutils.SampleCodeG101)
+		})
+
+		It("should work for G102 samples", func() {
+			runner("G102", testutils.SampleCodeG102)
+		})
+
+		It("should work for G103 samples", func() {
+			runner("G103", testutils.SampleCodeG103)
+		})
+
+		It("should work for G104 samples", func() {
+			runner("G104", testutils.SampleCodeG104)
+		})
+
+	})
+
+})