add Error type and constants

errors.go

@@ -0,0 +1,12 @@
+package validate
+
+type Error string
+
+const (
+	EmptyRuleset     Error = "attempted to run a validator with an empty rule set"
+	ValidationFailed Error = "validation failed"
+)
+
+func (e Error) Error() string {
+	return string(e)
+}

validation.go

@@ -3,8 +3,6 @@ package validate
 import (
 	"context"
 	"encoding/json"
-	"errors"
-	"fmt"
 	"net/http"
 )
 
@@ -48,10 +46,9 @@ func Make(r *http.Request, rule ...Rule) *Validator {
 }
 
 // Run determines if the given rules are satisfied by the request.
-// A "perfect" outcome is `nil, nil`.
 func (v *Validator) Run() (Message, error) {
 	if len(v.Rules) == 0 {
-		return nil, fmt.Errorf("no rules defined on validator")
+		return nil, EmptyRuleset
 	}
 
 	vm := make(Message)
@@ -63,7 +60,7 @@ func (v *Validator) Run() (Message, error) {
 	}
 
 	if len(vm) > 0 {
-		return vm, errors.New("validation failed")
+		return vm, ValidationFailed
 	}
 
 	return nil, nil

validation_test.go

@@ -31,13 +31,14 @@ func TestCheckCreatesValidatorAndRunsIt(t *testing.T) {
 	}
 }
 
-func TestMakeReturnsErrorWithNoRules(t *testing.T) {
+func TestRunReturnsErrorIfNoRulesExist(t *testing.T) {
 	r, _ := http.NewRequest("GET", "localhost", nil)
 
 	validator := Make(r)
 
-	if _, err := validator.Run(); err == nil {
-		fmt.Println("no error returned from empty validator")
+	_, err := validator.Run()
+	if err != EmptyRuleset {
+		fmt.Println("expected `EmptyRuleset` error.")
 		t.FailNow()
 	}
 }