diff --git a/LrcParser.Tests/Extension/EnumerableExtensionsTest.cs b/LrcParser.Tests/Extension/EnumerableExtensionsTest.cs
index c9e97c4..43a4a39 100644
--- a/LrcParser.Tests/Extension/EnumerableExtensionsTest.cs
+++ b/LrcParser.Tests/Extension/EnumerableExtensionsTest.cs
@@ -15,7 +15,7 @@ public class EnumerableExtensionsTest
     public void TestGroupByContinuous(int[] values, int[] expected)
     {
         var groups = values.GroupByContinuous(x => x);
-        Assert.AreEqual(expected, groups.Select(x => x.Key));
+        Assert.That(groups.Select(x => x.Key), Is.EqualTo(expected));
     }
 
     [TestCase(new[] { "A", "B", "C" }, new[] { "A", "B", "C" })]
@@ -23,6 +23,6 @@ public void TestGroupByContinuous(int[] values, int[] expected)
     public void TestGroupByContinuous(string[] values, string[] expected)
     {
         var groups = values.GroupByContinuous(x => x);
-        Assert.AreEqual(expected, groups.Select(x => x.Key));
+        Assert.That(groups.Select(x => x.Key), Is.EqualTo(expected));
     }
 }
diff --git a/LrcParser.Tests/LrcParser.Tests.csproj b/LrcParser.Tests/LrcParser.Tests.csproj
index e1e37e4..0cd8d02 100644
--- a/LrcParser.Tests/LrcParser.Tests.csproj
+++ b/LrcParser.Tests/LrcParser.Tests.csproj
@@ -9,7 +9,7 @@
 
     <ItemGroup>
         <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.8.0" />
-        <PackageReference Include="NUnit" Version="3.13.3" />
+        <PackageReference Include="NUnit" Version="4.0.1" />
         <PackageReference Include="NUnit3TestAdapter" Version="4.5.0" />
     </ItemGroup>
 
diff --git a/LrcParser.Tests/Model/TextIndexTest.cs b/LrcParser.Tests/Model/TextIndexTest.cs
index 80ec53a..70a4c5f 100644
--- a/LrcParser.Tests/Model/TextIndexTest.cs
+++ b/LrcParser.Tests/Model/TextIndexTest.cs
@@ -14,7 +14,7 @@ public class TextIndexTest
     [TestCase("-1,start")]
     public void TestOperatorEqual(string textIndex1)
     {
-        Assert.AreEqual(TestCaseTextIndexHelper.ParseTextIndex(textIndex1), TestCaseTextIndexHelper.ParseTextIndex(textIndex1));
+        Assert.That(TestCaseTextIndexHelper.ParseTextIndex(textIndex1), Is.EqualTo(TestCaseTextIndexHelper.ParseTextIndex(textIndex1)));
     }
 
     [TestCase("-1,start", "1,start")]
@@ -25,7 +25,7 @@ public void TestOperatorEqual(string textIndex1)
     [TestCase("-2,end", "-2,start")]
     public void TestOperatorNotEqual(string textIndex1, string textIndex2)
     {
-        Assert.AreNotEqual(TestCaseTextIndexHelper.ParseTextIndex(textIndex1), TestCaseTextIndexHelper.ParseTextIndex(textIndex2));
+        Assert.That(TestCaseTextIndexHelper.ParseTextIndex(textIndex1), Is.Not.EqualTo(TestCaseTextIndexHelper.ParseTextIndex(textIndex2)));
     }
 
     [TestCase("1,start", "0,start", true)]
@@ -34,7 +34,7 @@ public void TestOperatorNotEqual(string textIndex1, string textIndex2)
     [TestCase("1,start", "1,end", false)]
     public void TestOperatorGreater(string textIndex1, string textIndex2, bool match)
     {
-        Assert.AreEqual(TestCaseTextIndexHelper.ParseTextIndex(textIndex1) > TestCaseTextIndexHelper.ParseTextIndex(textIndex2), match);
+        Assert.That(TestCaseTextIndexHelper.ParseTextIndex(textIndex1) > TestCaseTextIndexHelper.ParseTextIndex(textIndex2), Is.EqualTo(match));
     }
 
     [TestCase("1,start", "0,start", true)]
@@ -43,7 +43,7 @@ public void TestOperatorGreater(string textIndex1, string textIndex2, bool match
     [TestCase("1,start", "1,end", false)]
     public void TestOperatorGreaterOrEqual(string textIndex1, string textIndex2, bool match)
     {
-        Assert.AreEqual(TestCaseTextIndexHelper.ParseTextIndex(textIndex1) >= TestCaseTextIndexHelper.ParseTextIndex(textIndex2), match);
+        Assert.That(TestCaseTextIndexHelper.ParseTextIndex(textIndex1) >= TestCaseTextIndexHelper.ParseTextIndex(textIndex2), Is.EqualTo(match));
     }
 
     [TestCase("-1,start", "0,start", true)]
@@ -52,7 +52,7 @@ public void TestOperatorGreaterOrEqual(string textIndex1, string textIndex2, boo
     [TestCase("-1,start", "-2,end", false)]
     public void TestOperatorLess(string textIndex1, string textIndex2, bool match)
     {
-        Assert.AreEqual(TestCaseTextIndexHelper.ParseTextIndex(textIndex1) < TestCaseTextIndexHelper.ParseTextIndex(textIndex2), match);
+        Assert.That(TestCaseTextIndexHelper.ParseTextIndex(textIndex1) < TestCaseTextIndexHelper.ParseTextIndex(textIndex2), Is.EqualTo(match));
     }
 
     [TestCase("-1,start", "0,start", true)]
@@ -61,6 +61,6 @@ public void TestOperatorLess(string textIndex1, string textIndex2, bool match)
     [TestCase("-1,start", "-2,end", false)]
     public void TestOperatorLessOrEqual(string textIndex1, string textIndex2, bool match)
     {
-        Assert.AreEqual(TestCaseTextIndexHelper.ParseTextIndex(textIndex1) <= TestCaseTextIndexHelper.ParseTextIndex(textIndex2), match);
+        Assert.That(TestCaseTextIndexHelper.ParseTextIndex(textIndex1) <= TestCaseTextIndexHelper.ParseTextIndex(textIndex2), Is.EqualTo(match));
     }
 }
diff --git a/LrcParser.Tests/Parser/BaseLyricParserTest.cs b/LrcParser.Tests/Parser/BaseLyricParserTest.cs
index 17af525..51a6a1a 100644
--- a/LrcParser.Tests/Parser/BaseLyricParserTest.cs
+++ b/LrcParser.Tests/Parser/BaseLyricParserTest.cs
@@ -28,8 +28,8 @@ protected static void AreEqual(Song expected, Song actual)
 
     private static void areEqual(Lyric expected, Lyric actual)
     {
-        Assert.AreEqual(expected.Text, actual.Text);
-        Assert.AreEqual(expected.TimeTags, actual.TimeTags);
+        Assert.That(actual.Text, Is.EqualTo(expected.Text));
+        Assert.That(actual.TimeTags, Is.EqualTo(expected.TimeTags));
 
         var expectedRubies = expected.RubyTags;
         var actualRubies = actual.RubyTags;
@@ -43,9 +43,9 @@ private static void areEqual(Lyric expected, Lyric actual)
 
     private static void areEqual(RubyTag expected, RubyTag actual)
     {
-        Assert.AreEqual(expected.Text, actual.Text);
-        Assert.AreEqual(expected.TimeTags, actual.TimeTags);
-        Assert.AreEqual(expected.StartCharIndex, actual.StartCharIndex);
-        Assert.AreEqual(expected.EndCharIndex, actual.EndCharIndex);
+        Assert.That(actual.Text, Is.EqualTo(expected.Text));
+        Assert.That(actual.TimeTags, Is.EqualTo(expected.TimeTags));
+        Assert.That(actual.StartCharIndex, Is.EqualTo(expected.StartCharIndex));
+        Assert.That(actual.EndCharIndex, Is.EqualTo(expected.EndCharIndex));
     }
 }
diff --git a/LrcParser.Tests/Parser/Lrc/Lines/LrcLyricParserTest.cs b/LrcParser.Tests/Parser/Lrc/Lines/LrcLyricParserTest.cs
index ce74d18..517f38f 100644
--- a/LrcParser.Tests/Parser/Lrc/Lines/LrcLyricParserTest.cs
+++ b/LrcParser.Tests/Parser/Lrc/Lines/LrcLyricParserTest.cs
@@ -19,7 +19,7 @@ public class LrcLyricParserTest : BaseSingleLineParserTest<LrcLyricParser, LrcLy
     public void TestCanDecode(string text, bool expected)
     {
         var actual = CanDecode(text);
-        Assert.AreEqual(expected, actual);
+        Assert.That(actual, Is.EqualTo(expected));
     }
 
     [TestCase("[00:17:97]帰[00:18:37]り[00:18:55]道[00:18:94]は[00:19:22]", "帰り道は", new[] { "[0,start]:17970", "[1,start]:18370", "[2,start]:18550", "[3,start]:18940", "[3,end]:19220" })]
@@ -37,8 +37,8 @@ public void TestDecode(string lyric, string text, string[] timeTags)
         };
         var actual = Decode(lyric);
 
-        Assert.AreEqual(expected.Text, actual.Text);
-        Assert.AreEqual(expected.TimeTags, actual.TimeTags);
+        Assert.That(actual.Text, Is.EqualTo(expected.Text));
+        Assert.That(actual.TimeTags, Is.EqualTo(expected.TimeTags));
     }
 
     [TestCase("帰り道は", new[] { "[0,start]:17970", "[1,start]:18370", "[2,start]:18550", "[3,start]:18940", "[3,end]:19220" }, "[00:17.97]帰[00:18.37]り[00:18.55]道[00:18.94]は[00:19.22]")]
@@ -55,6 +55,6 @@ public void TestEncode(string text, string[] timeTags, string expected)
         };
         var actual = Encode(lyric);
 
-        Assert.AreEqual(expected, actual);
+        Assert.That(actual, Is.EqualTo(expected));
     }
 }
diff --git a/LrcParser.Tests/Parser/Lrc/Lines/LrcRubyParserTest.cs b/LrcParser.Tests/Parser/Lrc/Lines/LrcRubyParserTest.cs
index 201975d..18fab03 100644
--- a/LrcParser.Tests/Parser/Lrc/Lines/LrcRubyParserTest.cs
+++ b/LrcParser.Tests/Parser/Lrc/Lines/LrcRubyParserTest.cs
@@ -19,7 +19,7 @@ public class LrcRubyParserTest : BaseSingleLineParserTest<LrcRubyParser, LrcRuby
     public void TestCanDecode(string text, bool expected)
     {
         var actual = CanDecode(text);
-        Assert.AreEqual(expected, actual);
+        Assert.That(actual, Is.EqualTo(expected));
     }
 
     [TestCase("@Ruby1=帰,かえ,[00:53:19],[01:24:77]", "帰", "かえ", new string[] { }, 53190, 84770)]
@@ -39,11 +39,11 @@ public void TestDecode(string rubyTag, string parent, string ruby, string[] time
         };
         var actual = Decode(rubyTag);
 
-        Assert.AreEqual(expected.Ruby, actual.Ruby);
-        Assert.AreEqual(expected.Parent, actual.Parent);
-        Assert.AreEqual(expected.TimeTags, actual.TimeTags);
-        Assert.AreEqual(expected.StartTime, actual.StartTime);
-        Assert.AreEqual(expected.EndTime, actual.EndTime);
+        Assert.That(actual.Ruby, Is.EqualTo(expected.Ruby));
+        Assert.That(actual.Parent, Is.EqualTo(expected.Parent));
+        Assert.That(actual.TimeTags, Is.EqualTo(expected.TimeTags));
+        Assert.That(actual.StartTime, Is.EqualTo(expected.StartTime));
+        Assert.That(actual.EndTime, Is.EqualTo(expected.EndTime));
     }
 
     [TestCase("帰", "かえ", new string[] { }, 53190, 84770, "@Ruby1=帰,かえ,[00:53.19],[01:24.77]")]
@@ -63,6 +63,6 @@ public void TestEncode(string parent, string ruby, string[] timeTags, int? start
         };
         var actual = Encode(rubyTag);
 
-        Assert.AreEqual(expected, actual);
+        Assert.That(actual, Is.EqualTo(expected));
     }
 }
diff --git a/LrcParser.Tests/Parser/Lrc/LrcParserTest.cs b/LrcParser.Tests/Parser/Lrc/LrcParserTest.cs
index bf11e37..e51c364 100644
--- a/LrcParser.Tests/Parser/Lrc/LrcParserTest.cs
+++ b/LrcParser.Tests/Parser/Lrc/LrcParserTest.cs
@@ -763,6 +763,6 @@ private void checkEncode(Song song, string[] lrcTexts)
     {
         var expected = string.Join('\n', lrcTexts);
         var actual = Encode(song);
-        Assert.AreEqual(expected, actual);
+        Assert.That(actual, Is.EqualTo(expected));
     }
 }
diff --git a/LrcParser.Tests/Parser/Lrc/Utils/LrcTimedTextUtilsTest.cs b/LrcParser.Tests/Parser/Lrc/Utils/LrcTimedTextUtilsTest.cs
index 8b26b74..97af4c2 100644
--- a/LrcParser.Tests/Parser/Lrc/Utils/LrcTimedTextUtilsTest.cs
+++ b/LrcParser.Tests/Parser/Lrc/Utils/LrcTimedTextUtilsTest.cs
@@ -23,8 +23,8 @@ public void TestDecode(string text, string expectedText, string[] expectedTimeTa
     {
         var (actualText, actualTimeTags) = LrcTimedTextUtils.TimedTextToObject(text);
 
-        Assert.AreEqual(expectedText, actualText);
-        Assert.AreEqual(TestCaseTagHelper.ParseTimeTags(expectedTimeTags), actualTimeTags);
+        Assert.That(actualText, Is.EqualTo(expectedText));
+        Assert.That(actualTimeTags, Is.EqualTo(TestCaseTagHelper.ParseTimeTags(expectedTimeTags)));
     }
 
     [TestCase("帰り道は", new[] { "[0,start]:17970", "[1,start]:18370", "[2,start]:18550", "[3,start]:18940", "[3,end]:19220" }, "[00:17.97]帰[00:18.37]り[00:18.55]道[00:18.94]は[00:19.22]")]
@@ -38,6 +38,6 @@ public void TestEncode(string text, string[] timeTags, string expected)
     {
         var actual = LrcTimedTextUtils.ToTimedText(text, TestCaseTagHelper.ParseTimeTags(timeTags));
 
-        Assert.AreEqual(expected, actual);
+        Assert.That(actual, Is.EqualTo(expected));
     }
 }
diff --git a/LrcParser.Tests/Parser/Lrc/Utils/TimeTagUtilsTest.cs b/LrcParser.Tests/Parser/Lrc/Utils/TimeTagUtilsTest.cs
index 3aef036..38d53fc 100644
--- a/LrcParser.Tests/Parser/Lrc/Utils/TimeTagUtilsTest.cs
+++ b/LrcParser.Tests/Parser/Lrc/Utils/TimeTagUtilsTest.cs
@@ -13,7 +13,7 @@ public void TestTimeTagToMillionSecond(string timeTag, int millionSecond)
     {
         var actual = TimeTagUtils.TimeTagToMillionSecond(timeTag);
 
-        Assert.AreEqual(millionSecond, actual);
+        Assert.That(actual, Is.EqualTo(millionSecond));
     }
 
     [TestCase(1000, "[00:01.00]")]
@@ -21,6 +21,6 @@ public void TestTimeTagToMillionSecond(int millionSecond, string timeTag)
     {
         var actual = TimeTagUtils.MillionSecondToTimeTag(millionSecond);
 
-        Assert.AreEqual(timeTag, actual);
+        Assert.That(actual, Is.EqualTo(timeTag));
     }
 }
diff --git a/LrcParser.Tests/Parser/LyricParserTest.cs b/LrcParser.Tests/Parser/LyricParserTest.cs
index d054498..8664f3e 100644
--- a/LrcParser.Tests/Parser/LyricParserTest.cs
+++ b/LrcParser.Tests/Parser/LyricParserTest.cs
@@ -20,7 +20,7 @@ public class LyricParserTest : BaseLyricParserTest<LyricParserTest.TestLyricPars
     public void TestDecodeWithEmptyFile(string lrcText)
     {
         var actual = Decode(lrcText);
-        Assert.IsEmpty(actual.Lyrics);
+        Assert.That(actual.Lyrics, Is.Empty);
     }
 
     [TestCase("karaoke\nカラオケ", new[] { "karaoke", "カラオケ" })]
@@ -30,10 +30,10 @@ public void TestDecodeWithEmptyFile(string lrcText)
     [TestCase("karaoke\nカラオケ\n", new[] { "karaoke", "カラオケ" })]
     [TestCase("karaoke\rカラオケ\r", new[] { "karaoke", "カラオケ" })]
     [TestCase("karaoke\r\nカラオケ\r\n", new[] { "karaoke", "カラオケ" })]
-    public void TestChangeNewLine(string lrcText, string[] lyrics)
+    public void TestChangeNewLine(string lrcText, string[] expected)
     {
         var actual = Decode(lrcText);
-        Assert.AreEqual(lyrics, actual.Lyrics.Select(x => x.Text));
+        Assert.That(actual.Lyrics.Select(x => x.Text), Is.EqualTo(expected));
     }
 
     public class TestLyricParser : LyricParser
diff --git a/LrcParser.Tests/Utils/TextIndexUtilsTest.cs b/LrcParser.Tests/Utils/TextIndexUtilsTest.cs
index b5578ad..26cb43f 100644
--- a/LrcParser.Tests/Utils/TextIndexUtilsTest.cs
+++ b/LrcParser.Tests/Utils/TextIndexUtilsTest.cs
@@ -18,7 +18,7 @@ public void TestToCharIndex(int index, IndexState state, int expected)
         var textIndex = new TextIndex(index, state);
 
         int actual = TextIndexUtils.ToCharIndex(textIndex);
-        Assert.AreEqual(expected, actual);
+        Assert.That(actual, Is.EqualTo(expected));
     }
 
     [TestCase(0, IndexState.Start, 0)]
@@ -30,7 +30,7 @@ public void TestToGapIndex(int index, IndexState state, int expected)
         var textIndex = new TextIndex(index, state);
 
         int actual = TextIndexUtils.ToGapIndex(textIndex);
-        Assert.AreEqual(expected, actual);
+        Assert.That(actual, Is.EqualTo(expected));
     }
 
     [TestCase(IndexState.Start, 1, -1, 1)]
@@ -42,6 +42,6 @@ public void TestGetValueByState(IndexState state, object startValue, object endV
         var textIndex = new TextIndex(0, state);
 
         object actual = TextIndexUtils.GetValueByState(textIndex, startValue, endValue);
-        Assert.AreEqual(expected, actual);
+        Assert.That(actual, Is.EqualTo(expected));
     }
 }
diff --git a/LrcParser.Tests/Utils/TypeUtilsTest.cs b/LrcParser.Tests/Utils/TypeUtilsTest.cs
index 583d035..59eeae9 100644
--- a/LrcParser.Tests/Utils/TypeUtilsTest.cs
+++ b/LrcParser.Tests/Utils/TypeUtilsTest.cs
@@ -13,31 +13,31 @@ public class TypeUtilsTest
     public void TestChangeTypeToSameType()
     {
         // test string
-        Assert.AreEqual("123", TypeUtils.ChangeType<string>("123"));
+        Assert.That(TypeUtils.ChangeType<string>("123"), Is.EqualTo("123"));
 
         // test number
-        Assert.AreEqual(456, TypeUtils.ChangeType<int>(456));
+        Assert.That(TypeUtils.ChangeType<int>(456), Is.EqualTo(456));
 
         // test another number
-        Assert.AreEqual(789f, TypeUtils.ChangeType<float>(789f));
+        Assert.That(TypeUtils.ChangeType<float>(789f), Is.EqualTo(789f));
 
         // test class, should use same instance.
         var testClass = new TestClass();
-        Assert.AreEqual(testClass, TypeUtils.ChangeType<TestClass>(testClass));
+        Assert.That(TypeUtils.ChangeType<TestClass>(testClass), Is.EqualTo(testClass));
     }
 
     [Test]
     public void TestChangeTypeToDifferentType()
     {
         // test convert to number
-        Assert.AreEqual(Convert.ToDouble(123), TypeUtils.ChangeType<double>(123));
+        Assert.That(TypeUtils.ChangeType<double>(123), Is.EqualTo(Convert.ToDouble(123)));
 
         // test convert to string
-        Assert.AreEqual(Convert.ToString(123), TypeUtils.ChangeType<string>(123));
+        Assert.That(TypeUtils.ChangeType<string>(123), Is.EqualTo(Convert.ToString(123)));
 
         // test convert to nullable
-        Assert.AreEqual(123, TypeUtils.ChangeType<double?>(123d));
-        Assert.AreEqual(default(double?), TypeUtils.ChangeType<double?>(null));
+        Assert.That(TypeUtils.ChangeType<double?>(123d), Is.EqualTo(123));
+        Assert.That(TypeUtils.ChangeType<double?>(null), Is.EqualTo(default(double?)));
     }
 
     private class TestClass