log entire content to see which assertion fails

src/libraries/Common/tests/TestUtilities/System/AssertExtensions.cs

@@ -499,6 +499,17 @@ public static void AtLeastOneEquals<T>(T expected1, T expected2, T value)
                 throw new XunitException($"Expected: {expected1} || {expected2}{Environment.NewLine}Actual: {value}");
         }
 
+        /// <summary>
+        /// Compares two strings, logs entire content if they are not equal.
+        /// </summary>
+        public static void Equal(string expected, string actual)
+        {
+            if (!expected.Equals(actual))
+            {
+                throw new AssertActualExpectedException(expected, actual, "Provided strings were not equal!");
+            }
+        }
+
         public delegate void AssertThrowsActionReadOnly<T>(ReadOnlySpan<T> span);
 
         public delegate void AssertThrowsAction<T>(Span<T> span);

src/libraries/System.Diagnostics.Process/tests/ProcessStreamReadTests.cs

@@ -82,7 +82,7 @@ public void TestAsyncErrorStream_SynchronizingObject(bool invokeRequired)
             p.WaitForExit(); // This ensures async event handlers are finished processing.
 
             const string Expected = RemotelyInvokable.TestConsoleApp + " started error stream" + RemotelyInvokable.TestConsoleApp + " closed error stream";
-            Assert.Equal(Expected, sb.ToString());
+            AssertExtensions.Equal(Expected, sb.ToString());
             Assert.Equal(invokeRequired ? 3 : 0, invokeCalled);
         }