Add indentation setting for Encoder (#386)

Fixes #371

marshal_test.go

@@ -44,6 +44,19 @@ Zstring = "Hello"
   String2 = "One"
 `)
 
+var basicTestTomlCustomIndentation = []byte(`Ystrlist = ["Howdy","Hey There"]
+Zstring = "Hello"
+
+[[Wsublist]]
+	String2 = "Two"
+
+[[Wsublist]]
+	String2 = "Three"
+
+[Xsubdoc]
+	String2 = "One"
+`)
+
 var basicTestTomlOrdered = []byte(`Zstring = "Hello"
 Ystrlist = ["Howdy","Hey There"]
 
@@ -207,6 +220,26 @@ func TestBasicMarshal(t *testing.T) {
 	}
 }
 
+func TestBasicMarshalCustomIndentation(t *testing.T) {
+	var result bytes.Buffer
+	err := NewEncoder(&result).Indentation("\t").Encode(basicTestData)
+	if err != nil {
+		t.Fatal(err)
+	}
+	expected := basicTestTomlCustomIndentation
+	if !bytes.Equal(result.Bytes(), expected) {
+		t.Errorf("Bad marshal: expected\n-----\n%s\n-----\ngot\n-----\n%s\n-----\n", expected, result.Bytes())
+	}
+}
+
+func TestBasicMarshalWrongIndentation(t *testing.T) {
+	var result bytes.Buffer
+	err := NewEncoder(&result).Indentation("  \n").Encode(basicTestData)
+	if err.Error() != "invalid indentation: must only contains space or tab characters" {
+		t.Error("expect err:invalid indentation: must only contains space or tab characters but got:", err)
+	}
+}
+
 func TestBasicMarshalOrdered(t *testing.T) {
 	var result bytes.Buffer
 	err := NewEncoder(&result).Order(OrderPreserve).Encode(basicTestData)