Change return for errdefs.getImplementer()

The types defined in the errdefs package do not
satisfy the `error` interface, because they do not
implement `Error()`.

Instead of returning the matched interface, return
the original error.

When matching _multiple_ interfaces/types, Golang doesn't complain:

    func getImplementer(err error) error {
        switch e := err.(type) {
        case
            ErrNotFound,
            ErrInvalidParameter:
            return e
        default:
            return err
        }
    }

But matching a single interface/type:

    func getImplementer(err error) error {
        switch e := err.(type) {
        case
            ErrNotFound:
            return e
        default:
            return err
        }
    }

Produces an error:

    cannot use e (type ErrNotFound) as type error in return argument: ErrNotFound does not implement error (missing Error method)

Return the original `err` instead of the matched interface/type instead.

Also added some additional tests

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

errdefs/helpers_test.go

@@ -12,6 +12,9 @@ type causal interface {
 }
 
 func TestNotFound(t *testing.T) {
+	if IsNotFound(errTest) {
+		t.Fatalf("did not expect not found error, got %T", errTest)
+	}
 	e := NotFound(errTest)
 	if !IsNotFound(e) {
 		t.Fatalf("expected not found error, got: %T", e)
@@ -22,6 +25,9 @@ func TestNotFound(t *testing.T) {
 }
 
 func TestConflict(t *testing.T) {
+	if IsConflict(errTest) {
+		t.Fatalf("did not expect conflcit error, got %T", errTest)
+	}
 	e := Conflict(errTest)
 	if !IsConflict(e) {
 		t.Fatalf("expected conflcit error, got: %T", e)
@@ -32,6 +38,9 @@ func TestConflict(t *testing.T) {
 }
 
 func TestForbidden(t *testing.T) {
+	if IsForbidden(errTest) {
+		t.Fatalf("did not expect forbidden error, got %T", errTest)
+	}
 	e := Forbidden(errTest)
 	if !IsForbidden(e) {
 		t.Fatalf("expected forbidden error, got: %T", e)
@@ -42,6 +51,9 @@ func TestForbidden(t *testing.T) {
 }
 
 func TestInvalidParameter(t *testing.T) {
+	if IsInvalidParameter(errTest) {
+		t.Fatalf("did not expect invalid argument error, got %T", errTest)
+	}
 	e := InvalidParameter(errTest)
 	if !IsInvalidParameter(e) {
 		t.Fatalf("expected invalid argument error, got %T", e)
@@ -52,6 +64,9 @@ func TestInvalidParameter(t *testing.T) {
 }
 
 func TestNotImplemented(t *testing.T) {
+	if IsNotImplemented(errTest) {
+		t.Fatalf("did not expect not implemented error, got %T", errTest)
+	}
 	e := NotImplemented(errTest)
 	if !IsNotImplemented(e) {
 		t.Fatalf("expected not implemented error, got %T", e)
@@ -62,6 +77,9 @@ func TestNotImplemented(t *testing.T) {
 }
 
 func TestNotModified(t *testing.T) {
+	if IsNotModified(errTest) {
+		t.Fatalf("did not expect not modified error, got %T", errTest)
+	}
 	e := NotModified(errTest)
 	if !IsNotModified(e) {
 		t.Fatalf("expected not modified error, got %T", e)
@@ -72,6 +90,9 @@ func TestNotModified(t *testing.T) {
 }
 
 func TestAlreadyExists(t *testing.T) {
+	if IsAlreadyExists(errTest) {
+		t.Fatalf("did not expect already exists error, got %T", errTest)
+	}
 	e := AlreadyExists(errTest)
 	if !IsAlreadyExists(e) {
 		t.Fatalf("expected already exists error, got %T", e)
@@ -82,6 +103,9 @@ func TestAlreadyExists(t *testing.T) {
 }
 
 func TestUnauthorized(t *testing.T) {
+	if IsUnauthorized(errTest) {
+		t.Fatalf("did not expect unauthorized error, got %T", errTest)
+	}
 	e := Unauthorized(errTest)
 	if !IsUnauthorized(e) {
 		t.Fatalf("expected unauthorized error, got %T", e)
@@ -92,6 +116,9 @@ func TestUnauthorized(t *testing.T) {
 }
 
 func TestUnknown(t *testing.T) {
+	if IsUnknown(errTest) {
+		t.Fatalf("did not expect unknown error, got %T", errTest)
+	}
 	e := Unknown(errTest)
 	if !IsUnknown(e) {
 		t.Fatalf("expected unknown error, got %T", e)
@@ -102,9 +129,12 @@ func TestUnknown(t *testing.T) {
 }
 
 func TestCancelled(t *testing.T) {
+	if IsCancelled(errTest) {
+		t.Fatalf("did not expect cancelled error, got %T", errTest)
+	}
 	e := Cancelled(errTest)
 	if !IsCancelled(e) {
-		t.Fatalf("expected canclled error, got %T", e)
+		t.Fatalf("expected cancelled error, got %T", e)
 	}
 	if cause := e.(causal).Cause(); cause != errTest {
 		t.Fatalf("causual should be errTest, got: %v", cause)
@@ -112,6 +142,9 @@ func TestCancelled(t *testing.T) {
 }
 
 func TestDeadline(t *testing.T) {
+	if IsDeadline(errTest) {
+		t.Fatalf("did not expect deadline error, got %T", errTest)
+	}
 	e := Deadline(errTest)
 	if !IsDeadline(e) {
 		t.Fatalf("expected deadline error, got %T", e)
@@ -121,7 +154,10 @@ func TestDeadline(t *testing.T) {
 	}
 }
 
-func TestIsDataLoss(t *testing.T) {
+func TestDataLoss(t *testing.T) {
+	if IsDataLoss(errTest) {
+		t.Fatalf("did not expect data loss error, got %T", errTest)
+	}
 	e := DataLoss(errTest)
 	if !IsDataLoss(e) {
 		t.Fatalf("expected data loss error, got %T", e)
@@ -130,3 +166,16 @@ func TestIsDataLoss(t *testing.T) {
 		t.Fatalf("causual should be errTest, got: %v", cause)
 	}
 }
+
+func TestUnavailable(t *testing.T) {
+	if IsUnavailable(errTest) {
+		t.Fatalf("did not expect unavaillable error, got %T", errTest)
+	}
+	e := Unavailable(errTest)
+	if !IsUnavailable(e) {
+		t.Fatalf("expected unavaillable error, got %T", e)
+	}
+	if cause := e.(causal).Cause(); cause != errTest {
+		t.Fatalf("causual should be errTest, got: %v", cause)
+	}
+}

errdefs/is.go

@@ -21,7 +21,7 @@ func getImplementer(err error) error {
 		ErrDeadline,
 		ErrDataLoss,
 		ErrUnknown:
-		return e
+		return err
 	case causer:
 		return getImplementer(e.Cause())
 	default: