refactored expander and ref resolver for readability (#135)

[NO CHANGE IN FUNCTIONALITY]

* refactored associated units tests for readability
* reshuffled resolver funcs and associated tests to a dedicated file
* removed panic() in ResolveRef (now return error) [used by go-swagger]

Signed-off-by: Frederic BIDON <fredbi@yahoo.com>

Author: fredbi

cache_test.go

@@ -0,0 +1,31 @@
+package spec
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestDefaultResolutionCache(t *testing.T) {
+	jsonSchema := MustLoadJSONSchemaDraft04()
+	swaggerSchema := MustLoadSwagger20Schema()
+
+	cache := defaultResolutionCache()
+
+	sch, ok := cache.Get("not there")
+	assert.False(t, ok)
+	assert.Nil(t, sch)
+
+	sch, ok = cache.Get("http://swagger.io/v2/schema.json")
+	assert.True(t, ok)
+	assert.Equal(t, swaggerSchema, sch)
+
+	sch, ok = cache.Get("http://json-schema.org/draft-04/schema")
+	assert.True(t, ok)
+	assert.Equal(t, jsonSchema, sch)
+
+	cache.Set("something", "here")
+	sch, ok = cache.Get("something")
+	assert.True(t, ok)
+	assert.Equal(t, "here", sch)
+}

errors.go

@@ -0,0 +1,18 @@
+package spec
+
+import "errors"
+
+var (
+	// ErrUnknownTypeForReference indicates that a resolved reference was found in an unsupported container type
+	ErrUnknownTypeForReference = errors.New("unknown type for the resolved reference")
+
+	// ErrResolveRefNeedsAPointer indicates that a $ref target must be a valid JSON pointer
+	ErrResolveRefNeedsAPointer = errors.New("resolve ref: target needs to be a pointer")
+
+	// ErrDerefUnsupportedType indicates that a resolved reference was found in an unsupported container type.
+	// At the moment, $ref are supported only inside: schemas, parameters, responses, path items
+	ErrDerefUnsupportedType = errors.New("deref: unsupported type")
+
+	// ErrExpandUnsupportedType indicates that $ref expansion is attempted on some invalid type
+	ErrExpandUnsupportedType = errors.New("expand: unsupported type. Input should be of type *Parameter or *Response")
+)