diff --git a/src/test/java/io/github/brenoepics/MentionExtractorTest.kt b/src/test/java/io/github/brenoepics/MentionExtractorTest.kt
index 920127f..6499d0a 100644
--- a/src/test/java/io/github/brenoepics/MentionExtractorTest.kt
+++ b/src/test/java/io/github/brenoepics/MentionExtractorTest.kt
@@ -85,4 +85,66 @@ class MentionExtractorTest {
 
         assertEquals(setOf("user1", "user2"), mentions)
     }
+
+    @Test
+    fun `extract mentions from null text`() {
+        val pattern = MentionPattern().defaultPattern()
+        val extractor = MentionExtractor.Builder().pattern(pattern).build()
+
+        val text = null
+        val mentions = extractor.fromString(text)
+
+        assertTrue(mentions.isEmpty())
+    }
+
+    @Test
+    fun `extract mentions from empty text`() {
+        val pattern = MentionPattern().defaultPattern()
+        val extractor = MentionExtractor.Builder().pattern(pattern).build()
+
+        val text = ""
+        val mentions = extractor.fromString(text)
+
+        assertTrue(mentions.isEmpty())
+    }
+
+    @Test
+    fun `check if null text contains mention`() {
+        val pattern = MentionPattern().defaultPattern()
+        val extractor = MentionExtractor.Builder().pattern(pattern).build()
+
+        val text = null
+
+        assertFalse(extractor.containsMention(text))
+    }
+
+    @Test
+    fun `check if empty text contains mention`() {
+        val pattern = MentionPattern().defaultPattern()
+        val extractor = MentionExtractor.Builder().pattern(pattern).build()
+
+        val text = ""
+
+        assertFalse(extractor.containsMention(text))
+    }
+
+    @Test
+    fun `count mentions in null text`() {
+        val pattern = MentionPattern().defaultPattern()
+        val extractor = MentionExtractor.Builder().pattern(pattern).build()
+
+        val text = null
+
+        assertEquals(0, extractor.countMentions(text))
+    }
+
+    @Test
+    fun `count mentions in empty text`() {
+        val pattern = MentionPattern().defaultPattern()
+        val extractor = MentionExtractor.Builder().pattern(pattern).build()
+
+        val text = ""
+
+        assertEquals(0, extractor.countMentions(text))
+    }
 }
diff --git a/src/test/java/io/github/brenoepics/MentionPatternTest.kt b/src/test/java/io/github/brenoepics/MentionPatternTest.kt
index 388f5a6..7d8b8b4 100644
--- a/src/test/java/io/github/brenoepics/MentionPatternTest.kt
+++ b/src/test/java/io/github/brenoepics/MentionPatternTest.kt
@@ -2,6 +2,7 @@ package io.github.brenoepics
 
 import org.junit.jupiter.api.Assertions.assertTrue
 import org.junit.jupiter.api.Test
+import kotlin.test.assertFalse
 
 class MentionPatternTest {
 
@@ -30,6 +31,16 @@ class MentionPatternTest {
         assertTrue(pattern.matcher("@user@example.net").matches())
     }
 
+    @Test
+    fun `withUnderscores should match mentions with underscores`() {
+        val pattern = MentionPattern().withUnderscores().build()
+        assertTrue(pattern.matcher("@user_name").matches())
+        assertTrue(pattern.matcher("@username").matches())
+        assertTrue(!pattern.matcher("@user-name").matches())
+        assertTrue(pattern.matcher("@username123").matches())
+        assertTrue(pattern.matcher("@user_name_123").matches())
+    }
+
     @Test
     fun `defaultPattern should match any word character after '@'`() {
         val pattern = MentionPattern().defaultPattern().build()
@@ -49,4 +60,34 @@ class MentionPatternTest {
         assertTrue(pattern.matcher("@username123").matches())
         assertTrue(pattern.matcher("@user_name_123").matches())
     }
+
+    @Test
+    fun `defaultPattern should not match null or empty strings`() {
+        val pattern = MentionPattern().defaultPattern().build()
+        assertFalse(pattern.matcher("").matches())
+    }
+
+    @Test
+    fun `withSpecialChars should not match null or empty strings`() {
+        val pattern = MentionPattern().withSpecialChars().build()
+        assertFalse(pattern.matcher("").matches())
+    }
+
+    @Test
+    fun `withEmailLike should not match null or empty strings`() {
+        val pattern = MentionPattern().withEmailLike().build()
+        assertFalse(pattern.matcher("").matches())
+    }
+
+    @Test
+    fun `withUnderscores should not match null or empty strings`() {
+        val pattern = MentionPattern().withUnderscores().build()
+        assertFalse(pattern.matcher("").matches())
+    }
+
+    @Test
+    fun `customPattern should not match null or empty strings`() {
+        val pattern = MentionPattern().customPattern("@([A-Za-z0-9_]+)").build()
+        assertFalse(pattern.matcher("").matches())
+    }
 }