simplify testing

testing/assert/error.go

@@ -0,0 +1,38 @@
+package assert
+
+func (this *Assert) Error(value error) *ErrorSubject {
+	valueStr := ""
+	if value != nil {
+		valueStr = value.Error()
+	}
+	return &ErrorSubject{
+		Subject: Subject{
+			a:    this,
+			disp: valueStr,
+		},
+		value: value,
+	}
+}
+
+type ErrorSubject struct {
+	Subject
+	value error
+}
+
+func (subject *ErrorSubject) Equals(expectation error) {
+	if subject.value != expectation {
+		subject.Fail("is equal to", expectation.Error())
+	}
+}
+
+func (subject *ErrorSubject) IsNil() {
+	if subject.value != nil {
+		subject.Fail("is", "nil")
+	}
+}
+
+func (subject *ErrorSubject) IsNotNil() {
+	if subject.value == nil {
+		subject.Fail("is not", "nil")
+	}
+}