refactor: focus around Render/Compact/Pretty/NewWith functions

This is yet another drastic refactor of public API and concepts.
Hopefully the last one, as I'm now fairly happy with things.

xml_test.go

@@ -32,7 +32,6 @@ func (mxm *mockXMLMarshaler) MarshalXML(
 func TestXML_Render(t *testing.T) {
 	tests := []struct {
 		name      string
-		pretty    bool
 		prefix    string
 		indent    string
 		value     any
@@ -41,8 +40,7 @@ func TestXML_Render(t *testing.T) {
 		wantErrIs []error
 	}{
 		{
-			name:   "simple object without pretty",
-			pretty: false,
+			name: "simple object",
 			value: struct {
 				XMLName xml.Name `xml:"user"`
 				Age     int      `xml:"age"`
@@ -50,28 +48,7 @@ func TestXML_Render(t *testing.T) {
 			want: `<user><age>30</age></user>`,
 		},
 		{
-			name:   "simple object with pretty",
-			pretty: true,
-			value: struct {
-				XMLName xml.Name `xml:"user"`
-				Age     int      `xml:"age"`
-			}{Age: 30},
-			want: "<user>\n  <age>30</age>\n</user>",
-		},
-		{
-			name:   "pretty with prefix and indent",
-			pretty: true,
-			prefix: "//",
-			indent: "\t",
-			value: struct {
-				XMLName xml.Name `xml:"user"`
-				Age     int      `xml:"age"`
-			}{Age: 30},
-			want: "//<user>\n//\t<age>30</age>\n//</user>",
-		},
-		{
-			name:   "prefix and indent without pretty",
-			pretty: false,
+			name:   "ignores indent without pretty",
 			prefix: "//",
 			indent: "\t",
 			value: struct {
@@ -93,7 +70,6 @@ func TestXML_Render(t *testing.T) {
 		},
 		{
 			name:      "invalid value",
-			pretty:    false,
 			value:     make(chan int),
 			wantErr:   "render: failed: xml: unsupported type: chan int",
 			wantErrIs: []error{Err, ErrFailed},
@@ -103,7 +79,6 @@ func TestXML_Render(t *testing.T) {
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
 			x := &XML{
-				Pretty: tt.pretty,
 				Prefix: tt.prefix,
 				Indent: tt.indent,
 			}
@@ -126,3 +101,82 @@ func TestXML_Render(t *testing.T) {
 		})
 	}
 }
+
+func TestXML_RenderPretty(t *testing.T) {
+	tests := []struct {
+		name      string
+		prefix    string
+		indent    string
+		value     any
+		want      string
+		wantErr   string
+		wantErrIs []error
+	}{
+		{
+			name: "simple object",
+			value: struct {
+				XMLName xml.Name `xml:"user"`
+				Age     int      `xml:"age"`
+			}{Age: 30},
+			want: "<user>\n  <age>30</age>\n</user>",
+		},
+		{
+			name:   "uses prefix and indent",
+			prefix: "//",
+			indent: "\t",
+			value: struct {
+				XMLName xml.Name `xml:"user"`
+				Age     int      `xml:"age"`
+			}{Age: 30},
+			want: "//<user>\n//\t<age>30</age>\n//</user>",
+		},
+		{
+			name:  "implements xml.Marshaler",
+			value: &mockXMLMarshaler{elm: "test string"},
+			want:  "<mockXMLMarshaler>test string</mockXMLMarshaler>",
+		},
+		{
+			name:      "error from xml.Marshaler",
+			value:     &mockXMLMarshaler{err: errors.New("mock error")},
+			wantErr:   "render: failed: mock error",
+			wantErrIs: []error{Err, ErrFailed},
+		},
+		{
+			name:      "invalid value",
+			value:     make(chan int),
+			wantErr:   "render: failed: xml: unsupported type: chan int",
+			wantErrIs: []error{Err, ErrFailed},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			x := &XML{
+				Prefix: tt.prefix,
+				Indent: tt.indent,
+			}
+			var buf bytes.Buffer
+
+			err := x.RenderPretty(&buf, tt.value)
+			got := buf.String()
+
+			if tt.wantErr != "" {
+				assert.EqualError(t, err, tt.wantErr)
+			}
+			for _, e := range tt.wantErrIs {
+				assert.ErrorIs(t, err, e)
+			}
+
+			if tt.wantErr == "" && len(tt.wantErrIs) == 0 {
+				assert.NoError(t, err)
+				assert.Equal(t, tt.want, got)
+			}
+		})
+	}
+}
+
+func TestXML_Formats(t *testing.T) {
+	h := &XML{}
+
+	assert.Equal(t, []string{"xml"}, h.Formats())
+}