Switch to ginkgo/gomega for tests

This switches over to ginkgo/gomega for tests, which makes writing
certain tests easier/more fluent in the future.

vendor/github.com/onsi/gomega/matchers/have_prefix_matcher.go

@@ -0,0 +1,36 @@
+package matchers
+
+import (
+	"fmt"
+
+	"github.com/onsi/gomega/format"
+)
+
+type HavePrefixMatcher struct {
+	Prefix string
+	Args   []interface{}
+}
+
+func (matcher *HavePrefixMatcher) Match(actual interface{}) (success bool, err error) {
+	actualString, ok := toString(actual)
+	if !ok {
+		return false, fmt.Errorf("HavePrefix matcher requires a string or stringer.  Got:\n%s", format.Object(actual, 1))
+	}
+	prefix := matcher.prefix()
+	return len(actualString) >= len(prefix) && actualString[0:len(prefix)] == prefix, nil
+}
+
+func (matcher *HavePrefixMatcher) prefix() string {
+	if len(matcher.Args) > 0 {
+		return fmt.Sprintf(matcher.Prefix, matcher.Args...)
+	}
+	return matcher.Prefix
+}
+
+func (matcher *HavePrefixMatcher) FailureMessage(actual interface{}) (message string) {
+	return format.Message(actual, "to have prefix", matcher.prefix())
+}
+
+func (matcher *HavePrefixMatcher) NegatedFailureMessage(actual interface{}) (message string) {
+	return format.Message(actual, "not to have prefix", matcher.prefix())
+}