feat: add the ability to manually specify the want value

This is necessary to separate data in table tests when there are few
cases with big data and there are cases with short data that are better
represented in the table.

Perhaps this method is not a good idea, since the test data is mixed,
but perhaps this opportunity will do itself well in practice.

golden.go

@@ -46,6 +46,10 @@ type Tool struct {
 	flag      *bool
 	prefix    string
 	extension string
+	// want it stores manually set expected data, if it is nil, then the
+	// data will be read from the files, otherwise the value from this
+	// field will be taken.
+	want []byte
 
 	mkdirAll  func(path string, perm os.FileMode) error
 	readFile  func(filename string) ([]byte, error)
@@ -116,6 +120,14 @@ func SetTest(t TestingTB) Tool {
 	return _golden.SetTest(t)
 }
 
+// SetWant a place to set the expected want manually.
+// want value it stores manually set expected data, if it is nil,
+// then the data will be read from the files, otherwise the value
+// from this field will be taken.
+func SetWant(t TestingTB, bs []byte) Tool {
+	return _golden.SetTest(t).SetWant(bs)
+}
+
 // Assert is a tool to compare the actual value obtained in the test and
 // the value from the golden file. Also, built-in functionality for
 // updating golden files using the command line flag.
@@ -191,10 +203,17 @@ func JSONEq(tb TestingTB, got string) Conclusion {
 // Read is a functional for reading both input and golden files using
 // the appropriate target.
 func (t Tool) Read() (bs []byte) {
-	const f = "golden: read the value of nil since it is not found file: %s"
+	if t.want != nil {
+		t.test.Logf("golden: read the value from the want field")
+		bs = make([]byte, len(t.want))
+		copy(bs, t.want)
+
+		return bs
+	}
 
 	bs, err := t.readFile(t.path())
 	if os.IsNotExist(err) {
+		const f = "golden: read the value of nil since it is not found file: %s"
 		t.test.Logf(f, t.path())
 		return nil
 	} else if err != nil {
@@ -232,6 +251,20 @@ func (t Tool) SetTest(tb TestingTB) Tool {
 	return t
 }
 
+// SetWant a place to set the expected want manually.
+// want value it stores manually set expected data, if it is nil,
+// then the data will be read from the files, otherwise the value
+// from this field will be taken.
+func (t Tool) SetWant(bs []byte) Tool {
+	t.want = nil
+	if bs != nil {
+		t.want = make([]byte, len(bs))
+		copy(t.want, bs)
+	}
+
+	return t
+}
+
 // Update functional reviewer is the need to update the golden files
 // and doing it.
 func (t Tool) Update(bs []byte) {

golden_test.go

@@ -476,6 +476,12 @@ func TestTool_Read(t *testing.T) {
 			}
 		})
 	}
+	t.Run("with-set-want-field", func(t *testing.T) {
+		tb := &bufferTB{name: t.Name()}
+		tool := SetWant(tb, []byte(t.Name()))
+		assert.Equal(t, t.Name(), string(tool.Read()))
+		_goldie.SetTest(t).Assert(tb.Bytes())
+	})
 }
 
 func TestTool_Run(t *testing.T) {

testdata/TestTool_Read/with-set-want-field.golden

@@ -0,0 +1 @@
+golden: read the value from the want field