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/contain_substring_matcher.go

@@ -0,0 +1,38 @@
+package matchers
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/onsi/gomega/format"
+)
+
+type ContainSubstringMatcher struct {
+	Substr string
+	Args   []interface{}
+}
+
+func (matcher *ContainSubstringMatcher) Match(actual interface{}) (success bool, err error) {
+	actualString, ok := toString(actual)
+	if !ok {
+		return false, fmt.Errorf("ContainSubstring matcher requires a string or stringer.  Got:\n%s", format.Object(actual, 1))
+	}
+
+	return strings.Contains(actualString, matcher.stringToMatch()), nil
+}
+
+func (matcher *ContainSubstringMatcher) stringToMatch() string {
+	stringToMatch := matcher.Substr
+	if len(matcher.Args) > 0 {
+		stringToMatch = fmt.Sprintf(matcher.Substr, matcher.Args...)
+	}
+	return stringToMatch
+}
+
+func (matcher *ContainSubstringMatcher) FailureMessage(actual interface{}) (message string) {
+	return format.Message(actual, "to contain substring", matcher.stringToMatch())
+}
+
+func (matcher *ContainSubstringMatcher) NegatedFailureMessage(actual interface{}) (message string) {
+	return format.Message(actual, "not to contain substring", matcher.stringToMatch())
+}