errcount: factor errcount abstraction from operations

lib/errcount/errcount_test.go

@@ -0,0 +1,27 @@
+package errcount
+
+import (
+	"errors"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestErrCount(t *testing.T) {
+	ec := New()
+	assert.Equal(t, nil, ec.Err("none"))
+
+	e1 := errors.New("one")
+	ec.Add(e1)
+
+	err := ec.Err("stuff")
+	assert.True(t, errors.Is(err, e1), err)
+	assert.Equal(t, "stuff: one", err.Error())
+
+	e2 := errors.New("two")
+	ec.Add(e2)
+
+	err = ec.Err("stuff")
+	assert.True(t, errors.Is(err, e2), err)
+	assert.Equal(t, "stuff: 2 errors: last error: two", err.Error())
+}