Omit empty <properties> tag when there are no properties.

Go doesn't omit empty parent tags for empty values[1], so we'll work
around this for now by creating a pointer to the property slice.

[1]: https://github.com/golang/go/issues/7233.

pkg/junit/junit.go

@@ -48,15 +48,21 @@ type Testsuite struct {
 	Time      string `xml:"time,attr"`                // duration in seconds
 	Timestamp string `xml:"timestamp,attr,omitempty"` // date and time in ISO8601
 
-	Properties []Property `xml:"properties>property,omitempty"`
-	Testcases  []Testcase `xml:"testcase,omitempty"`
-	SystemOut  *Output    `xml:"system-out,omitempty"`
-	SystemErr  *Output    `xml:"system-err,omitempty"`
+	Properties *[]Property `xml:"properties>property,omitempty"`
+	Testcases  []Testcase  `xml:"testcase,omitempty"`
+	SystemOut  *Output     `xml:"system-out,omitempty"`
+	SystemErr  *Output     `xml:"system-err,omitempty"`
 }
 
 // AddProperty adds a property with the given name and value to this Testsuite.
 func (t *Testsuite) AddProperty(name, value string) {
-	t.Properties = append(t.Properties, Property{Name: name, Value: value})
+	prop := Property{Name: name, Value: value}
+	if t.Properties == nil {
+		t.Properties = &[]Property{prop}
+		return
+	}
+	props := append(*t.Properties, prop)
+	t.Properties = &props
 }
 
 // AddTestcase adds Testcase tc to this Testsuite.

pkg/junit/junit_test.go

@@ -27,7 +27,7 @@ func TestMarshalUnmarshal(t *testing.T) {
 				Skipped:    1,
 				Time:       "12.345",
 				Timestamp:  "2012-03-09T14:38:06+01:00",
-				Properties: []Property{{"key", "value"}},
+				Properties: properties("key", "value"),
 				Testcases: []Testcase{
 					{
 						Name:      "test1",
@@ -62,3 +62,14 @@ func TestMarshalUnmarshal(t *testing.T) {
 		t.Errorf("Unmarshal result incorrect, diff (-want +got):\n%s\n", diff)
 	}
 }
+
+func properties(keyvals ...string) *[]Property {
+	if len(keyvals)%2 != 0 {
+		panic("invalid keyvals specified")
+	}
+	var props []Property
+	for i := 0; i < len(keyvals); i += 2 {
+		props = append(props, Property{keyvals[i], keyvals[i+1]})
+	}
+	return &props
+}