It is empty, causing these tests to fail:

• System.Tests.EnvironmentStackTrace.StackTraceDoesNotStartWithInternalFrame
  fails with System.NullReferenceException.

Failure Message:

[FAIL] System.Tests.EnvironmentStackTrace.StackTraceDoesNotStartWithInternalFrame
System.NullReferenceException : Object reference not set to an instance of an object.
   at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)

Calling Code:

public void StackTraceDoesNotStartWithInternalFrame()
        {
             string stackTrace = Environment.StackTrace;

             // Find first line of the stacktrace and verify that it is Environment.get_StackTrace itself, not an internal frame
             string firstFrame = new StringReader(stackTrace).ReadLine();

             Assert.True(firstFrame.IndexOf("System.Environment.get_StackTrace()") != -1);
        }

For Browser WASM, Environment.StackTrace is empty, which leads to a null return in StringReader.cs's method ReadLine. Therefore, it cannot access IndexOf.

• System.Diagnostics.TraceSourceTests.TraceEventCacheClassTests.CallstackTest_NotEmpty
  Assert.NotEmpty() Failure
  at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)

• System.Diagnostics.TraceSourceTests.TraceEventCacheClassTests.CallstackTest_ContainsExpectedFrames
  Assert.Contains() Failure
  Not found: System.Environment.get_StackTrace()

• System.Diagnostics.TraceSourceTests.TraceListenerClassTests.WriteFooterTest_Callstack
  Assert.Contains() Failure
  Not found: WriteFooterTest_Callstack