microsoft · Evangelink · Oct 8, 2025 · Oct 8, 2025 · Oct 8, 2025 · Oct 8, 2025
diff --git a/src/TestFramework/TestFramework/Assertions/Assert.That.cs b/src/TestFramework/TestFramework/Assertions/Assert.That.cs
diff --git a/src/TestFramework/TestFramework/Resources/FrameworkMessages.resx b/src/TestFramework/TestFramework/Resources/FrameworkMessages.resx
@@ -1,17 +1,17 @@
 <?xml version="1.0" encoding="utf-8"?>
 <root>
-  <!-- 
-    Microsoft ResX Schema 
-    
+  <!--
+    Microsoft ResX Schema
+
     Version 2.0
-    
-    The primary goals of this format is to allow a simple XML format 
-    that is mostly human readable. The generation and parsing of the 
-    various data types are done through the TypeConverter classes 
+
+    The primary goals of this format is to allow a simple XML format
+    that is mostly human readable. The generation and parsing of the
+    various data types are done through the TypeConverter classes
     associated with the data types.
-    
+
     Example:
-    
+
     ... ado.net/XML headers & schema ...
     <resheader name="resmimetype">text/microsoft-resx</resheader>
     <resheader name="version">2.0</resheader>
@@ -26,36 +26,36 @@
         <value>[base64 mime encoded string representing a byte array form of the .NET Framework object]</value>
         <comment>This is a comment</comment>
     </data>
-                
-    There are any number of "resheader" rows that contain simple 
+
+    There are any number of "resheader" rows that contain simple
     name/value pairs.
-    
-    Each data row contains a name, and value. The row also contains a 
-    type or mimetype. Type corresponds to a .NET class that support 
-    text/value conversion through the TypeConverter architecture. 
-    Classes that don't support this are serialized and stored with the 
+
+    Each data row contains a name, and value. The row also contains a
+    type or mimetype. Type corresponds to a .NET class that support
+    text/value conversion through the TypeConverter architecture.
+    Classes that don't support this are serialized and stored with the
     mimetype set.
-    
-    The mimetype is used for serialized objects, and tells the 
-    ResXResourceReader how to depersist the object. This is currently not 
+
+    The mimetype is used for serialized objects, and tells the
+    ResXResourceReader how to depersist the object. This is currently not
     extensible. For a given mimetype the value must be set accordingly:
-    
-    Note - application/x-microsoft.net.object.binary.base64 is the format 
-    that the ResXResourceWriter will generate, however the reader can 
+
+    Note - application/x-microsoft.net.object.binary.base64 is the format
+    that the ResXResourceWriter will generate, however the reader can
     read any of the formats listed below.
-    
+
     mimetype: application/x-microsoft.net.object.binary.base64
-    value   : The object must be serialized with 
+    value   : The object must be serialized with
             : System.Runtime.Serialization.Formatters.Binary.BinaryFormatter
             : and then encoded with base64 encoding.
-    
+
     mimetype: application/x-microsoft.net.object.soap.base64
-    value   : The object must be serialized with 
+    value   : The object must be serialized with
             : System.Runtime.Serialization.Formatters.Soap.SoapFormatter
             : and then encoded with base64 encoding.
 
     mimetype: application/x-microsoft.net.object.bytearray.base64
-    value   : The object must be serialized into a byte array 
+    value   : The object must be serialized into a byte array
             : using a System.ComponentModel.TypeConverter
             : and then encoded with base64 encoding.
     -->
@@ -387,4 +387,7 @@ Actual: {2}</value>
   <data name="IsInRangeMaxValueMustBeGreaterThanOrEqualMinValue" xml:space="preserve">
     <value>The maximum value must be greater than or equal to the minimum value.</value>
   </data>
+  <data name="AssertThatFailedToEvaluate" xml:space="preserve">
+    <value>&lt;Failed to evaluate&gt;</value>
+  </data>
 </root>
diff --git a/src/TestFramework/TestFramework/Resources/xlf/FrameworkMessages.cs.xlf b/src/TestFramework/TestFramework/Resources/xlf/FrameworkMessages.cs.xlf
@@ -327,8 +327,11 @@ Skutečnost: {2}</target>
         <source>Element(s) &lt;{0}&gt; is/are not present in the collection.</source>
         <target state="translated">Elementy &lt;{0}&gt; se v kolekci nenachází.</target>
         <note />
-      </trans-unit>
-      <trans-unit id="StartsWithFail">
+      </trans-unit>      <trans-unit id="AssertThatFailedToEvaluate">
+        <source>&lt;Failed to evaluate&gt;</source>
+        <target state="new">&lt;Failed to evaluate&gt;</target>
+        <note />
+      </trans-unit>      <trans-unit id="StartsWithFail">
         <source>String '{0}' does not start with string '{1}'. {2}</source>
         <target state="translated">Řetězec „{0}“ nezačíná řetězcem „{1}“. {2}</target>
         <note />

diff --git a/src/TestFramework/TestFramework/Resources/xlf/FrameworkMessages.de.xlf b/src/TestFramework/TestFramework/Resources/xlf/FrameworkMessages.de.xlf
@@ -327,8 +327,11 @@ Tatsächlich: {2}</target>
         <source>Element(s) &lt;{0}&gt; is/are not present in the collection.</source>
         <target state="translated">Element(e) &lt;{0}&gt; ist/sind in der Auflistung nicht vorhanden.</target>
         <note />
-      </trans-unit>
-      <trans-unit id="StartsWithFail">
+      </trans-unit>      <trans-unit id="AssertThatFailedToEvaluate">
+        <source>&lt;Failed to evaluate&gt;</source>
+        <target state="new">&lt;Failed to evaluate&gt;</target>
+        <note />
+      </trans-unit>      <trans-unit id="StartsWithFail">
         <source>String '{0}' does not start with string '{1}'. {2}</source>
         <target state="translated">Die Zeichenfolge „{0}“ beginnt nicht mit der Zeichenfolge „{1}“. {2}</target>
         <note />

diff --git a/src/TestFramework/TestFramework/Resources/xlf/FrameworkMessages.es.xlf b/src/TestFramework/TestFramework/Resources/xlf/FrameworkMessages.es.xlf
@@ -328,6 +328,11 @@ Real: {2}</target>
         <target state="translated">Los elementos &lt;{0}&gt; no están presentes en la colección.</target>
         <note />
       </trans-unit>
+      <trans-unit id="AssertThatFailedToEvaluate">
+        <source>&lt;Failed to evaluate&gt;</source>
+        <target state="new">&lt;Failed to evaluate&gt;</target>
+        <note />
+      </trans-unit>
       <trans-unit id="StartsWithFail">
         <source>String '{0}' does not start with string '{1}'. {2}</source>
         <target state="translated">La cadena "{0}" no empieza con la cadena "{1}". {2}</target>

diff --git a/src/TestFramework/TestFramework/Resources/xlf/FrameworkMessages.fr.xlf b/src/TestFramework/TestFramework/Resources/xlf/FrameworkMessages.fr.xlf
@@ -327,8 +327,11 @@ Réel : {2}</target>
         <source>Element(s) &lt;{0}&gt; is/are not present in the collection.</source>
         <target state="translated">L’élément ou les éléments &lt;{0}&gt; n’est ou ne sont pas présent(s) dans la collection.</target>
         <note />
-      </trans-unit>
-      <trans-unit id="StartsWithFail">
+      </trans-unit>      <trans-unit id="AssertThatFailedToEvaluate">
+        <source>&lt;Failed to evaluate&gt;</source>
+        <target state="new">&lt;Failed to evaluate&gt;</target>
+        <note />
+      </trans-unit>      <trans-unit id="StartsWithFail">
         <source>String '{0}' does not start with string '{1}'. {2}</source>
         <target state="translated">La chaîne '{0}' ne commence pas par la chaîne '{1}'. {2}</target>
         <note />

diff --git a/src/TestFramework/TestFramework/Resources/xlf/FrameworkMessages.it.xlf b/src/TestFramework/TestFramework/Resources/xlf/FrameworkMessages.it.xlf
@@ -328,6 +328,11 @@ Effettivo: {2}</target>
         <target state="translated">Gli elementi &lt;{0}&gt; non sono presenti nella raccolta.</target>
         <note />
       </trans-unit>
+      <trans-unit id="AssertThatFailedToEvaluate">
+        <source>&lt;Failed to evaluate&gt;</source>
+        <target state="new">&lt;Failed to evaluate&gt;</target>
+        <note />
+      </trans-unit>
       <trans-unit id="StartsWithFail">
         <source>String '{0}' does not start with string '{1}'. {2}</source>
         <target state="translated">La stringa '{0}' non inizia con la stringa '{1}'. {2}</target>

diff --git a/src/TestFramework/TestFramework/Resources/xlf/FrameworkMessages.ja.xlf b/src/TestFramework/TestFramework/Resources/xlf/FrameworkMessages.ja.xlf
@@ -327,8 +327,11 @@ Actual: {2}</source>
         <source>Element(s) &lt;{0}&gt; is/are not present in the collection.</source>
         <target state="translated">要素 &lt;{0}&gt; がコレクション内に存在しません。</target>
         <note />
-      </trans-unit>
-      <trans-unit id="StartsWithFail">
+      </trans-unit>      <trans-unit id="AssertThatFailedToEvaluate">
+        <source>&lt;Failed to evaluate&gt;</source>
+        <target state="new">&lt;Failed to evaluate&gt;</target>
+        <note />
+      </trans-unit>      <trans-unit id="StartsWithFail">
         <source>String '{0}' does not start with string '{1}'. {2}</source>
         <target state="translated">文字列 '{0}' は文字列 '{1}' で始まりません。{2}</target>
         <note />

diff --git a/src/TestFramework/TestFramework/Resources/xlf/FrameworkMessages.ko.xlf b/src/TestFramework/TestFramework/Resources/xlf/FrameworkMessages.ko.xlf
@@ -327,8 +327,11 @@ Actual: {2}</source>
         <source>Element(s) &lt;{0}&gt; is/are not present in the collection.</source>
         <target state="translated">컬렉션에 &lt;{0}&gt; 요소가 없습니다.</target>
         <note />
-      </trans-unit>
-      <trans-unit id="StartsWithFail">
+      </trans-unit>      <trans-unit id="AssertThatFailedToEvaluate">
+        <source>&lt;Failed to evaluate&gt;</source>
+        <target state="new">&lt;Failed to evaluate&gt;</target>
+        <note />
+      </trans-unit>      <trans-unit id="StartsWithFail">
         <source>String '{0}' does not start with string '{1}'. {2}</source>
         <target state="translated">'{0}' 문자열이 '{1}' 문자열로 시작되지 않습니다. {2}</target>
         <note />

diff --git a/src/TestFramework/TestFramework/Resources/xlf/FrameworkMessages.pl.xlf b/src/TestFramework/TestFramework/Resources/xlf/FrameworkMessages.pl.xlf
@@ -327,8 +327,11 @@ Rzeczywiste: {2}</target>
         <source>Element(s) &lt;{0}&gt; is/are not present in the collection.</source>
         <target state="translated">Elementy &lt;{0}&gt; nie występują w kolekcji.</target>
         <note />
-      </trans-unit>
-      <trans-unit id="StartsWithFail">
+      </trans-unit>      <trans-unit id="AssertThatFailedToEvaluate">
+        <source>&lt;Failed to evaluate&gt;</source>
+        <target state="new">&lt;Failed to evaluate&gt;</target>
+        <note />
+      </trans-unit>      <trans-unit id="StartsWithFail">
         <source>String '{0}' does not start with string '{1}'. {2}</source>
         <target state="translated">Ciąg „{0}” nie rozpoczyna się od ciągu „{1}”. {2}</target>
         <note />

diff --git a/src/TestFramework/TestFramework/Resources/xlf/FrameworkMessages.pt-BR.xlf b/src/TestFramework/TestFramework/Resources/xlf/FrameworkMessages.pt-BR.xlf
@@ -327,8 +327,11 @@ Real: {2}</target>
         <source>Element(s) &lt;{0}&gt; is/are not present in the collection.</source>
         <target state="translated">O(s) elemento(s) &lt;{0}&gt; não está/estão presente(s) na coleção.</target>
         <note />
-      </trans-unit>
-      <trans-unit id="StartsWithFail">
+      </trans-unit>      <trans-unit id="AssertThatFailedToEvaluate">
+        <source>&lt;Failed to evaluate&gt;</source>
+        <target state="new">&lt;Failed to evaluate&gt;</target>
+        <note />
+      </trans-unit>      <trans-unit id="StartsWithFail">
         <source>String '{0}' does not start with string '{1}'. {2}</source>
         <target state="translated">A cadeia de caracteres “{0}” não começa com a cadeia de caracteres “{1}”. {2}</target>
         <note />

diff --git a/src/TestFramework/TestFramework/Resources/xlf/FrameworkMessages.ru.xlf b/src/TestFramework/TestFramework/Resources/xlf/FrameworkMessages.ru.xlf
@@ -295,7 +295,7 @@ Actual: {2}</source>
     </source>
         <target state="translated">
       Не удается найти указанный член ({0}). Возможно, требуется снова создать закрытый метод доступа
-      либо член является закрытым и определенным на основе базового класса. Если справедливо последнее, то 
+      либо член является закрытым и определенным на основе базового класса. Если справедливо последнее, то
       необходимо передать тип, определяющий член, в конструктор для PrivateObject.
     </target>
         <note />
@@ -307,8 +307,8 @@ Actual: {2}</source>
       that defines the member into PrivateObject's constructor.
     </source>
         <target state="translated">
-      Не удается найти конструктор с указанной сигнатурой. Возможно, требуется снова создать закрытый 
-      метод доступа либо член является закрытым и определенным на основе базового класса. Если 
+      Не удается найти конструктор с указанной сигнатурой. Возможно, требуется снова создать закрытый
+      метод доступа либо член является закрытым и определенным на основе базового класса. Если
       справедливо последнее, то необходимо передать тип, определяющий член, в конструктор для PrivateObject.
     </target>
         <note />
@@ -328,6 +328,11 @@ Actual: {2}</source>
         <target state="translated">Элементы &lt;{0}&gt; отсутствуют в коллекции.</target>
         <note />
       </trans-unit>
+      <trans-unit id="AssertThatFailedToEvaluate">
+        <source>&lt;Failed to evaluate&gt;</source>
+        <target state="new">&lt;Failed to evaluate&gt;</target>
+        <note />
+      </trans-unit>
       <trans-unit id="StartsWithFail">
         <source>String '{0}' does not start with string '{1}'. {2}</source>
         <target state="translated">Строка "{0}" не начинается со строки "{1}". {2}</target>

diff --git a/src/TestFramework/TestFramework/Resources/xlf/FrameworkMessages.tr.xlf b/src/TestFramework/TestFramework/Resources/xlf/FrameworkMessages.tr.xlf
@@ -327,8 +327,11 @@ Gerçekte olan: {2}</target>
         <source>Element(s) &lt;{0}&gt; is/are not present in the collection.</source>
         <target state="translated">Öğe(ler) &lt;{0}&gt; koleksiyonda mevcut değildir.</target>
         <note />
-      </trans-unit>
-      <trans-unit id="StartsWithFail">
+      </trans-unit>      <trans-unit id="AssertThatFailedToEvaluate">
+        <source>&lt;Failed to evaluate&gt;</source>
+        <target state="new">&lt;Failed to evaluate&gt;</target>
+        <note />
+      </trans-unit>      <trans-unit id="StartsWithFail">
         <source>String '{0}' does not start with string '{1}'. {2}</source>
         <target state="translated">'{0}' dizesi, '{1}' dizesi ile başlamıyor. {2}</target>
         <note />

diff --git a/src/TestFramework/TestFramework/Resources/xlf/FrameworkMessages.zh-Hans.xlf b/src/TestFramework/TestFramework/Resources/xlf/FrameworkMessages.zh-Hans.xlf
@@ -328,6 +328,11 @@ Actual: {2}</source>
         <target state="translated">集合中不存在元素 &lt;{0}&gt;。</target>
         <note />
       </trans-unit>
+      <trans-unit id="AssertThatFailedToEvaluate">
+        <source>&lt;Failed to evaluate&gt;</source>
+        <target state="new">&lt;Failed to evaluate&gt;</target>
+        <note />
+      </trans-unit>
       <trans-unit id="StartsWithFail">
         <source>String '{0}' does not start with string '{1}'. {2}</source>
         <target state="translated">字符串 '{0}' 不以字符串 '{1}' 开头。{2}</target>

diff --git a/src/TestFramework/TestFramework/Resources/xlf/FrameworkMessages.zh-Hant.xlf b/src/TestFramework/TestFramework/Resources/xlf/FrameworkMessages.zh-Hant.xlf
@@ -328,6 +328,11 @@ Actual: {2}</source>
         <target state="translated">集合中不存在元素 &lt;{0}&gt;。</target>
         <note />
       </trans-unit>
+      <trans-unit id="AssertThatFailedToEvaluate">
+        <source>&lt;Failed to evaluate&gt;</source>
+        <target state="new">&lt;Failed to evaluate&gt;</target>
+        <note />
+      </trans-unit>
       <trans-unit id="StartsWithFail">
         <source>String '{0}' does not start with string '{1}'. {2}</source>
         <target state="translated">字串 '{0}' 不是以字串 '{1}' 開頭。{2}</target>

diff --git a/test/UnitTests/TestFramework.UnitTests/Assertions/AssertTests.That.cs b/test/UnitTests/TestFramework.UnitTests/Assertions/AssertTests.That.cs
@@ -479,10 +479,10 @@ public void That_NewExpression_ExtractsVariablesCorrectly()
             .WithMessage($"""
                 Assert.That(() => new DateTime(year, month, day) == DateTime.MinValue) failed.
                 Details:
-                  DateTime.MinValue = {DateTime.MinValue.ToString(CultureInfo.CurrentCulture)}
+                  DateTime.MinValue = {DateTime.MinValue.ToString(CultureInfo.InvariantCulture)}
                   day = 25
                   month = 12
-                  new DateTime(year, month, day) = {new DateTime(year, month, day).ToString(CultureInfo.CurrentCulture)}
+                  new DateTime(year, month, day) = {new DateTime(year, month, day).ToString(CultureInfo.InvariantCulture)}
                   year = 2023
                 """);
     }
@@ -1042,4 +1042,64 @@ public void That_WithNullConstantAndVariable_OnlyIncludesVariable()
               nullVariable = null
             """);
     }
+
+    public void That_DoesNotEvaluateTwice_WhenAssertionFails()
+    {
+        var box = new Box();
+
+        // If we evaluate twice, box.GetValueWithSideEffect() is called once on comparison, and once when message for assertion is built.
+        // We compare to 0 to force failure.
+        Action act = () => Assert.That(() => box.GetValueWithSideEffect() == 0);
+
+        // GetValueWithSideEffect() should report 1, which is the value when we evaluate only once.
+        act.Should().Throw<AssertFailedException>()
+            .WithMessage("""
+            Assert.That(() => box.GetValueWithSideEffect() == 0) failed.
+            Details:
+              box.GetValueWithSideEffect() = 1
+            """);
+
+        // We call again, this should be second call now.
+        box.GetValueWithSideEffect().Should().Be(2);
+    }
+
+    public void That_DoesNotEvaluateTwice_WhenAssertionFails_NoSideEffect()
+    {
+        int i = 1;
+        Action act = () => Assert.That(() => i + i == 0);
+
+        act.Should().Throw<AssertFailedException>()
+            .WithMessage("""
+            Assert.That(() => i + i == 0) failed.
+            Details:
+              i = 1
+            """);
+    }
+
+    public void That_DoesEvaluateTwice_WhenMethodIsLeaf()
+    {
+        var box = new Box();
+
+        // Compare to 0 to force failure.
+        Action act = () => Assert.That(() => box.GetValueWithSideEffect() + box.GetValueWithSideEffect() == 0);
+
+        act.Should().Throw<AssertFailedException>()
+            .WithMessage("""
+            Assert.That(() => box.GetValueWithSideEffect() + box.GetValueWithSideEffect() == 0) failed.
+            Details:
+              box.GetValueWithSideEffect() = 1
+              box.GetValueWithSideEffect() (2) = 2
+            """);
+    }
+
+    private class Box
+    {
+        private int _c;
+
+        public int GetValueWithSideEffect()
+        {
+            _c++;
+            return _c;
+        }
+    }
 }