com.cedarsoft.test.utils.CatchAllExceptionsRule Maven / Gradle / Ivy

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package com.cedarsoft.test.utils;

import org.junit.*;
import org.junit.rules.*;
import org.junit.runner.*;
import org.junit.runners.model.*;

import javax.annotation.Nonnull;
import javax.annotation.Nullable;
import java.io.PrintWriter;
import java.io.StringWriter;
import java.util.ArrayList;
import java.util.List;

/**
 * This rule catches exceptions on all threads and fails the test if such exceptions are caught
 *
 * @author Johannes Schneider ([email protected])
 */
public class CatchAllExceptionsRule implements TestRule {
  @Nullable
  private Thread.UncaughtExceptionHandler oldHandler;

  @Override
  public Statement apply( final Statement base, Description description ) {
    return new Statement() {
      @Override
      public void evaluate() throws Throwable {
        before();
        try {
          base.evaluate();
        } catch ( Throwable t ) {
          afterFailing();
          throw t;
        }

        afterSuccess();
      }
    };
  }

  private void before() {
    oldHandler = Thread.getDefaultUncaughtExceptionHandler();
    Thread.setDefaultUncaughtExceptionHandler( new Thread.UncaughtExceptionHandler() {
      @Override
      public void uncaughtException( Thread t, Throwable e ) {
        caught.add( e );
        if ( oldHandler != null ) {
          oldHandler.uncaughtException( t, e );
        }
      }
    } );
  }

  @Nonnull
  private final List caught = new ArrayList();

  private void afterSuccess() {
    Thread.setDefaultUncaughtExceptionHandler( oldHandler );

    if ( caught.isEmpty() ) {
      return;
    }

    throw new AssertionError( buildMessage() );
  }

  private String buildMessage() {
    StringBuilder builder = new StringBuilder();
    builder.append( caught.size() ).append( " exceptions thrown but not caught in other threads:\n" );

    for ( Throwable throwable : caught ) {
      builder.append( "---------------------\n" );

      StringWriter out = new StringWriter();
      throwable.printStackTrace( new PrintWriter( out ) );
      builder.append( out.toString() );
    }

    builder.append( "---------------------\n" );

    return builder.toString();
  }

  private void afterFailing() {
    Thread.setDefaultUncaughtExceptionHandler( oldHandler );
  }
}