Added typed error (#10)

* added typed error

* added test, changed Err name

* added common error type

* renamed Error

* implemented requested changes

gobreaker.go

@@ -3,6 +3,7 @@
 package gobreaker
 
 import (
+	"errors"
 	"fmt"
 	"sync"
 	"time"
@@ -18,6 +19,13 @@ const (
 	StateOpen
 )
 
+var (
+	// ErrTooManyRequests is returned when the CB state is half open and the requests count is over the cb maxRequests
+	ErrTooManyRequests = errors.New("too many requests")
+	// ErrOpenState is returned when the CB state is open
+	ErrOpenState = errors.New("circuit breaker is open")
+)
+
 // String implements stringer interface.
 func (s State) String() string {
 	switch s {
@@ -237,9 +245,9 @@ func (cb *CircuitBreaker) beforeRequest() (uint64, error) {
 	state, generation := cb.currentState(now)
 
 	if state == StateOpen {
-		return generation, cb.errorStateOpen()
+		return generation, ErrOpenState
 	} else if state == StateHalfOpen && cb.counts.Requests >= cb.maxRequests {
-		return generation, fmt.Errorf("too many requests")
+		return generation, ErrTooManyRequests
 	}
 
 	cb.counts.onRequest()
@@ -334,11 +342,3 @@ func (cb *CircuitBreaker) toNewGeneration(now time.Time) {
 		cb.expiry = zero
 	}
 }
-
-func (cb *CircuitBreaker) errorStateOpen() error {
-	if cb.name == "" {
-		return fmt.Errorf("circuit breaker is open")
-	}
-
-	return fmt.Errorf("circuit breaker '%s' is open", cb.name)
-}

gobreaker_test.go

@@ -346,11 +346,3 @@ func TestCircuitBreakerInParallel(t *testing.T) {
 	}
 	assert.Equal(t, Counts{total, total, 0, total, 0}, customCB.counts)
 }
-
-func TestErrorStateOpen(t *testing.T) {
-	err := defaultCB.errorStateOpen()
-	assert.Equal(t, "circuit breaker is open", err.Error())
-
-	err = customCB.errorStateOpen()
-	assert.Equal(t, "circuit breaker 'cb' is open", err.Error())
-}