Add basic unit tests for bbcode conversion

src/test/java/io/papermc/hangar/util/BBCodeConverterTest.java

@@ -0,0 +1,52 @@
+package io.papermc.hangar.util;
+
+import io.papermc.hangar.controller.util.BBCodeConverter;
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+public class BBCodeConverterTest {
+
+    private final BBCodeConverter converter = new BBCodeConverter();
+
+    @Test
+    void testDuplicates() {
+        String result = converter.convertToMarkdown("[b][s][b]Test[b]Tes[/b]t[/s][/b][/b]");
+        Assertions.assertEquals(result, "**~~TestTest~~**");
+    }
+
+    @Test
+    void testRemoved() {
+        String result = converter.convertToMarkdown("[list][size=4][color=red][user=kennytv]T[/size][center]e[font=upsidedown][/center]st[/font][/color][/user][/list]");
+        Assertions.assertEquals(result, "Test");
+    }
+
+    @Test
+    void testList() {
+        String result = converter.convertToMarkdown("[list]\n[*]Element 1\n[*]Element 2\n[/list]");
+        Assertions.assertEquals(result, "\n* Element 1\n* Element 2\n");
+    }
+
+    @Test
+    void testFormatting() {
+        String result = converter.convertToMarkdown("[b]I am bold [i]and cursive [s]and crossed out[/s][/i][/b]");
+        Assertions.assertEquals(result, "**I am bold *and cursive ~~and crossed out~~***");
+    }
+
+    @Test
+    void testImageAndUrl() {
+        String result = converter.convertToMarkdown("[img]imagelink[/img], [url=https://github.com/]click here[/url]");
+        Assertions.assertEquals(result, "![imagelink](imagelink), [click here](https://github.com/)");
+    }
+
+    @Test
+    void testCode() {
+        String result = converter.convertToMarkdown("[code]Codeblock![/code]");
+        Assertions.assertEquals(result, "```Codeblock!```");
+    }
+
+    @Test
+    void testAttachment() {
+        String result = converter.convertToMarkdown("[attach]100[/attach]");
+        Assertions.assertEquals(result, "![https://www.spigotmc.org/attachments/100](https://www.spigotmc.org/attachments/100)");
+    }
+}