diff --git a/ClosedXML/ClosedXML/ClosedXML_Tests/ClosedXML_Tests.csproj b/ClosedXML/ClosedXML/ClosedXML_Tests/ClosedXML_Tests.csproj
index dbc5325..0342658 100644
--- a/ClosedXML/ClosedXML/ClosedXML_Tests/ClosedXML_Tests.csproj
+++ b/ClosedXML/ClosedXML/ClosedXML_Tests/ClosedXML_Tests.csproj
@@ -85,8 +85,9 @@
       <Private>True</Private>
     </Reference>
     <Reference Include="Microsoft.CSharp" />
-    <Reference Include="nunit.framework">
-      <HintPath>..\packages\NUnit.2.6.3\lib\nunit.framework.dll</HintPath>
+    <Reference Include="nunit.framework, Version=3.4.1.0, Culture=neutral, PublicKeyToken=2638cd05610744eb, processorArchitecture=MSIL">
+      <HintPath>..\packages\NUnit.3.4.1\lib\net40\nunit.framework.dll</HintPath>
+      <Private>True</Private>
     </Reference>
     <Reference Include="System" />
     <Reference Include="System.ComponentModel.DataAnnotations" />
diff --git a/ClosedXML/ClosedXML/ClosedXML_Tests/Excel/RichText/XLRichStringTests.cs b/ClosedXML/ClosedXML/ClosedXML_Tests/Excel/RichText/XLRichStringTests.cs
index 062285b..729d680 100644
--- a/ClosedXML/ClosedXML/ClosedXML_Tests/Excel/RichText/XLRichStringTests.cs
+++ b/ClosedXML/ClosedXML/ClosedXML_Tests/Excel/RichText/XLRichStringTests.cs
@@ -597,7 +597,6 @@
         }
 
         [Test]
-        [ExpectedException(typeof (IndexOutOfRangeException))]
         public void Substring_IndexOutsideRange1()
         {
             IXLWorksheet ws = new XLWorkbook().Worksheets.Add("Sheet1");
@@ -605,11 +604,10 @@
 
             richString.AddText("Hello");
 
-            IXLFormattedText<IXLRichText> richText = richString.Substring(50);
+            Assert.That(() => richString.Substring(50), Throws.TypeOf<IndexOutOfRangeException>());
         }
 
         [Test]
-        [ExpectedException(typeof (IndexOutOfRangeException))]
         public void Substring_IndexOutsideRange2()
         {
             IXLWorksheet ws = new XLWorkbook().Worksheets.Add("Sheet1");
@@ -618,11 +616,10 @@
             richString.AddText("Hello");
             richString.AddText("World");
 
-            IXLFormattedText<IXLRichText> richText = richString.Substring(50);
+            Assert.That(() => richString.Substring(50), Throws.TypeOf<IndexOutOfRangeException>());
         }
 
         [Test]
-        [ExpectedException(typeof (IndexOutOfRangeException))]
         public void Substring_IndexOutsideRange3()
         {
             IXLWorksheet ws = new XLWorkbook().Worksheets.Add("Sheet1");
@@ -630,11 +627,10 @@
 
             richString.AddText("Hello");
 
-            IXLFormattedText<IXLRichText> richText = richString.Substring(1, 10);
+            Assert.That(() => richString.Substring(1, 10), Throws.TypeOf<IndexOutOfRangeException>());
         }
 
         [Test]
-        [ExpectedException(typeof (IndexOutOfRangeException))]
         public void Substring_IndexOutsideRange4()
         {
             IXLWorksheet ws = new XLWorkbook().Worksheets.Add("Sheet1");
@@ -643,7 +639,7 @@
             richString.AddText("Hello");
             richString.AddText("World");
 
-            IXLFormattedText<IXLRichText> richText = richString.Substring(5, 20);
+            Assert.That(() => richString.Substring(5, 20), Throws.TypeOf<IndexOutOfRangeException>());
         }
 
         /// <summary>
diff --git a/ClosedXML/ClosedXML/ClosedXML_Tests/packages.config b/ClosedXML/ClosedXML/ClosedXML_Tests/packages.config
index d47c16a..dcf0b39 100644
--- a/ClosedXML/ClosedXML/ClosedXML_Tests/packages.config
+++ b/ClosedXML/ClosedXML/ClosedXML_Tests/packages.config
@@ -1,6 +1,5 @@
 <?xml version="1.0" encoding="utf-8"?>
-
 <packages>
   <package id="DocumentFormat.OpenXml" version="2.5" targetFramework="net40" />
-  <package id="NUnit" version="2.6.3" targetFramework="net40" />
+  <package id="NUnit" version="3.4.1" targetFramework="net40" />
 </packages>
\ No newline at end of file