System.Diagnostics.Debug.AssertFailureException – Assertion failed

The System.Diagnostics.Debug.AssertFailureException with the message “Assertion failed” occurs in .NET when a debug assertion fails. This typically happens in debug builds when a condition checked by Debug.Assert evaluates to false. Assertions are used to validate assumptions in the code and help catch bugs during development.

Here’s a detailed explanation of the issue and how to resolve it:

Common Causes

Invalid Assumptions

The condition passed to Debug.Assert is false, indicating that an assumption in the code is incorrect.

Unexpected State

The application is in an unexpected state, causing the assertion to fail.

Debug-Only Checks

The assertion is only checked in debug builds, so the issue might not be apparent in release builds.

Incorrect Logic

The logic in the code leading up to the assertion is incorrect.

Solutions

1. Investigate the Assertion Failure

Examine the condition that caused the assertion to fail and determine why it evaluated to false. Example:

   int value = GetValue();
   Debug.Assert(value > 0, "Value must be greater than 0");

If the assertion fails, investigate why value is not greater than 0.

2. Fix the Underlying Issue

Correct the logic or state that caused the assertion to fail. Example:

   int value = GetValue();
   if (value <= 0)
   {
       throw new ArgumentException("Value must be greater than 0");
   }
   Debug.Assert(value > 0, "Value must be greater than 0");

3. Add Logging

Add logging to capture the state of the application when the assertion fails. Example:

   int value = GetValue();
   if (value <= 0)
   {
       Debug.WriteLine($"Assertion failed: value = {value}");
       Debug.Assert(false, "Value must be greater than 0");
   }

4. Use `Trace.Assert` for Release Builds

Use Trace.Assert if you want the assertion to be checked in both debug and release builds. Example:

   int value = GetValue();
   Trace.Assert(value > 0, "Value must be greater than 0");

5. Handle Edge Cases

Ensure the code handles edge cases and invalid inputs gracefully. Example:

   int value = GetValue();
   if (value <= 0)
   {
       value = 1; // Default to a valid value
   }
   Debug.Assert(value > 0, "Value must be greater than 0");

6. Review Unit Tests

Ensure unit tests cover the scenario that caused the assertion to fail. Example:

   [TestMethod]
   public void TestValueIsPositive()
   {
       int value = GetValue();
       Assert.IsTrue(value > 0, "Value must be greater than 0");
   }

Debugging Tips

Use the debugger to inspect the state of the application when the assertion fails.
Check the call stack to identify where the assertion was triggered.
Use logging to capture additional context about the failure.

Best Practices

Use assertions to validate assumptions and catch bugs during development.
Add meaningful messages to assertions to make debugging easier.
Handle edge cases and invalid inputs gracefully.
Use Trace.Assert for assertions that should be checked in release builds.

Example of Proper Assertion Usage

Debug Assertion

int value = GetValue();
Debug.Assert(value > 0, "Value must be greater than 0");

Trace Assertion

int value = GetValue();
Trace.Assert(value > 0, "Value must be greater than 0");

Handling Edge Cases

int value = GetValue();
if (value <= 0)
{
    value = 1; // Default to a valid value
}
Debug.Assert(value > 0, "Value must be greater than 0");

Adding Logging

int value = GetValue();
if (value <= 0)
{
    Debug.WriteLine($"Assertion failed: value = {value}");
    Debug.Assert(false, "Value must be greater than 0");
}