Move internal packages to an internal folder

For reference: https://go.dev/doc/go1.4#internalpackages

internal/reader/sanitizer/truncate_test.go

@@ -0,0 +1,64 @@
+// SPDX-FileCopyrightText: Copyright The Miniflux Authors. All rights reserved.
+// SPDX-License-Identifier: Apache-2.0
+
+package sanitizer
+
+import "testing"
+
+func TestTruncateHTMWithTextLowerThanLimitL(t *testing.T) {
+	input := `This is a <strong>bug 🐛</strong>.`
+	expected := `This is a bug 🐛.`
+	output := TruncateHTML(input, 50)
+
+	if expected != output {
+		t.Errorf(`Wrong output: %q != %q`, expected, output)
+	}
+}
+
+func TestTruncateHTMLWithTextAboveLimit(t *testing.T) {
+	input := `This is <strong>HTML</strong>.`
+	expected := `This…`
+	output := TruncateHTML(input, 4)
+
+	if expected != output {
+		t.Errorf(`Wrong output: %q != %q`, expected, output)
+	}
+}
+
+func TestTruncateHTMLWithUnicodeTextAboveLimit(t *testing.T) {
+	input := `This is a <strong>bike 🚲</strong>.`
+	expected := `This…`
+	output := TruncateHTML(input, 4)
+
+	if expected != output {
+		t.Errorf(`Wrong output: %q != %q`, expected, output)
+	}
+}
+
+func TestTruncateHTMLWithMultilineTextAboveLimit(t *testing.T) {
+	input := `
+		This is a <strong>bike
+		🚲</strong>.
+
+	`
+	expected := `This is a bike…`
+	output := TruncateHTML(input, 15)
+
+	if expected != output {
+		t.Errorf(`Wrong output: %q != %q`, expected, output)
+	}
+}
+
+func TestTruncateHTMLWithMultilineTextLowerThanLimit(t *testing.T) {
+	input := `
+		This is a <strong>bike
+ 🚲</strong>.
+
+	`
+	expected := `This is a bike 🚲.`
+	output := TruncateHTML(input, 20)
+
+	if expected != output {
+		t.Errorf(`Wrong output: %q != %q`, expected, output)
+	}
+}