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/*
 * Copyright (c) 2011 Google, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.google.common.truth;

import com.google.common.annotations.GwtIncompatible;
import org.junit.internal.AssumptionViolatedException;

/**
 * Provides a way to use Truth to perform JUnit "assumptions." An assumption is a check that, if
 * false, aborts (skips) the test. This is especially useful in JUnit theories, parameterized tests,
 * or other combinatorial tests where some subset of the combinations are simply not applicable for
 * testing.
 *
 * For example:
 *
 * 
{@code
 * import static com.google.common.truth.Truth.assertThat;
 * import static com.google.common.truth.TruthJUnit.assume;
 *
 * public void @Test testFoosAgainstBars {
 *   assume().that(foo).isNotNull();
 *   assume().that(bar).isNotNull();
 *   assertThat(foo.times(bar)).isEqualTo(blah);
 * }
 * }
 *
 * @author David Saff
 * @author Christian Gruber ([email protected])
 */
@GwtIncompatible("JUnit4")
public final class TruthJUnit {
  private static final FailureStrategy THROW_ASSUMPTION_ERROR =
      new FailureStrategy() {
        @Override
        public void fail(AssertionError failure) {
          ThrowableAssumptionViolatedException assumptionViolated =
              new ThrowableAssumptionViolatedException(failure.getMessage(), failure.getCause());
          assumptionViolated.setStackTrace(failure.getStackTrace());
          throw assumptionViolated;
        }
      };

  private static final StandardSubjectBuilder ASSUME =
      StandardSubjectBuilder.forCustomFailureStrategy(THROW_ASSUMPTION_ERROR);

  /**
   * Begins a call chain with the fluent Truth API. If the check made by the chain fails, it will
   * throw {@link AssumptionViolatedException}.
   */
  public static final StandardSubjectBuilder assume() {
    return ASSUME;
  }

  // TODO(diamondm): remove this and use org.junit.AssumptionViolatedException once we're on v4.12
  private static class ThrowableAssumptionViolatedException extends AssumptionViolatedException {
    public ThrowableAssumptionViolatedException(String message, Throwable throwable) {
      super(message);
      if (throwable != null) initCause(throwable);
    }
  }

  private TruthJUnit() {}
}