test internal/cerr package + add WrapString() to use a raw string

internal/cerr/cerr.go

@@ -16,6 +16,14 @@ func (err Error) Wrap(e error) *WrapError {
 	}
 }
 
+// WrapString returns a new error which wraps a new error created from a string.
+func (err Error) WrapString(e string) *WrapError {
+	return &WrapError{
+		base: err,
+		wrap: Error(e),
+	}
+}
+
 // WrapError is way to wrap errors recursively.
 type WrapError struct {
 	base error

internal/cerr/cerr_test.go

@@ -0,0 +1,57 @@
+package cerr
+
+import (
+	"errors"
+	"fmt"
+	"testing"
+)
+
+func TestConstError(t *testing.T) {
+	const cerr1 = Error("some-string")
+	const cerr2 = Error("some-other-string")
+	const cerr3 = Error("some-string") // same const value as @cerr1
+
+	if cerr1.Error() == cerr2.Error() {
+		t.Errorf("cerr1 should not be equal to cerr2 ('%s', '%s')", cerr1.Error(), cerr2.Error())
+	}
+	if cerr2.Error() == cerr3.Error() {
+		t.Errorf("cerr2 should not be equal to cerr3 ('%s', '%s')", cerr2.Error(), cerr3.Error())
+	}
+	if cerr1.Error() != cerr3.Error() {
+		t.Errorf("cerr1 should be equal to cerr3 ('%s', '%s')", cerr1.Error(), cerr3.Error())
+	}
+}
+
+func TestWrappedConstError(t *testing.T) {
+	const parent = Error("file error")
+
+	const readErrorConst = Error("cannot read file")
+	var wrappedReadError = parent.Wrap(readErrorConst)
+
+	expectedWrappedReadError := fmt.Sprintf("%s: %s", parent.Error(), readErrorConst.Error())
+	if wrappedReadError.Error() != expectedWrappedReadError {
+		t.Errorf("expected '%s' (got '%s')", wrappedReadError.Error(), expectedWrappedReadError)
+	}
+}
+func TestWrappedStandardError(t *testing.T) {
+	const parent = Error("file error")
+
+	var writeErrorStandard error = errors.New("cannot write file")
+	var wrappedWriteError = parent.Wrap(writeErrorStandard)
+
+	expectedWrappedWriteError := fmt.Sprintf("%s: %s", parent.Error(), writeErrorStandard.Error())
+	if wrappedWriteError.Error() != expectedWrappedWriteError {
+		t.Errorf("expected '%s' (got '%s')", wrappedWriteError.Error(), expectedWrappedWriteError)
+	}
+}
+func TestWrappedStringError(t *testing.T) {
+	const parent = Error("file error")
+
+	var closeErrorString string = "cannot close file"
+	var wrappedCloseError = parent.WrapString(closeErrorString)
+
+	expectedWrappedCloseError := fmt.Sprintf("%s: %s", parent.Error(), closeErrorString)
+	if wrappedCloseError.Error() != expectedWrappedCloseError {
+		t.Errorf("expected '%s' (got '%s')", wrappedCloseError.Error(), expectedWrappedCloseError)
+	}
+}