build: test LogError

Closes #34

build/error.go

@@ -40,6 +40,10 @@ func (e *ErrorList) Add(err Error) {
 	*e = append(*e, err)
 }
 
+func (e *ErrorList) AddAt(p src.Position, err error) {
+	e.Add(Error{p, err})
+}
+
 // addext appends an error to the list, tagged with the
 func (e *ErrorList) addext(err error) {
 	e.Add(exterr(err))
@@ -71,11 +75,11 @@ func (e ErrorList) Error() string {
 func LogError(l *log.Logger, err error, max int) {
 	if list, ok := err.(ErrorList); ok {
 		for i, e := range list {
-			l.Printf("%s\n", e)
 			if max > 0 && i == max {
 				l.Print("too many errors")
 				return
 			}
+			l.Printf("%s\n", e)
 		}
 	} else if err != nil {
 		l.Printf("%s\n", err)

build/error_test.go

@@ -0,0 +1,72 @@
+package build
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"log"
+	"testing"
+
+	"github.com/mmcloughlin/avo/src"
+)
+
+func TestLogErrorNil(t *testing.T) {
+	var buf bytes.Buffer
+	l := log.New(&buf, "prefix: ", 0)
+	LogError(l, nil, 0)
+	if buf.String() != "" {
+		t.Fatalf("should print nothing for nil error")
+	}
+}
+
+func TestLogErrorNonErrorList(t *testing.T) {
+	var buf bytes.Buffer
+	l := log.New(&buf, "prefix: ", 0)
+	err := errors.New("not an ErrorList")
+	LogError(l, err, 0)
+	got := buf.String()
+	expect := "prefix: " + err.Error() + "\n"
+	if got != expect {
+		t.Fatalf("got\t%q\nexpect\t%q\n", got, expect)
+	}
+}
+
+func TestLogErrorList(t *testing.T) {
+	var buf bytes.Buffer
+	l := log.New(&buf, "prefix: ", 0)
+
+	e := ErrorList{}
+	filename := "asm.go"
+	err := errors.New("some kind of error")
+	n := 7
+	for i := 1; i <= n; i++ {
+		p := src.Position{Filename: filename, Line: i}
+		e.AddAt(p, err)
+	}
+
+	expect := ""
+	// Unlimited print.
+	LogError(l, e, 0)
+	for i := 1; i <= n; i++ {
+		expect += fmt.Sprintf("prefix: %s:%d: some kind of error\n", filename, i)
+	}
+
+	// Max equal to number of errors.
+	LogError(l, e, n)
+	for i := 1; i <= n; i++ {
+		expect += fmt.Sprintf("prefix: %s:%d: some kind of error\n", filename, i)
+	}
+
+	// Max less than number of errors.
+	m := n / 2
+	LogError(l, e, m)
+	for i := 1; i <= m; i++ {
+		expect += fmt.Sprintf("prefix: %s:%d: some kind of error\n", filename, i)
+	}
+	expect += fmt.Sprintf("prefix: too many errors\n")
+
+	got := buf.String()
+	if got != expect {
+		t.Fatalf("got\n%s\nexpect\n%s\n", got, expect)
+	}
+}