RuleChainTest.java

package org.junit.rules;

import static java.util.Arrays.asList;
import static org.hamcrest.CoreMatchers.containsString;
import static org.hamcrest.CoreMatchers.equalTo;
import static org.hamcrest.MatcherAssert.assertThat;
import static org.junit.Assert.assertEquals;
import static org.junit.Assert.assertTrue;
import static org.junit.Assert.fail;
import static org.junit.experimental.results.PrintableResult.testResult;
import static org.junit.rules.RuleChain.outerRule;

import java.io.PrintWriter;
import java.io.StringWriter;
import java.util.ArrayList;
import java.util.List;

import org.junit.Rule;
import org.junit.Test;
import org.junit.internal.Throwables;
import org.junit.runner.Description;
import org.junit.runner.JUnitCore;
import org.junit.runner.Result;

public class RuleChainTest {
    private static final List<String> LOG = new ArrayList<String>();

    private static class LoggingRule extends TestWatcher {
        private final String label;

        public LoggingRule(String label) {
            this.label = label;
        }

        @Override
        protected void starting(Description description) {
            LOG.add("starting " + label);
        }

        @Override
        protected void finished(Description description) {
            LOG.add("finished " + label);
        }
    }

    public static class UseRuleChain {
        @Rule
        public final RuleChain chain = outerRule(new LoggingRule("outer rule"))
                .around(new LoggingRule("middle rule")).around(
                        new LoggingRule("inner rule"));

        @Test
        public void example() {
            assertTrue(true);
        }
    }

    @Test
    public void executeRulesInCorrectOrder() throws Exception {
        testResult(UseRuleChain.class);
        List<String> expectedLog = asList("starting outer rule",
                "starting middle rule", "starting inner rule",
                "finished inner rule", "finished middle rule",
                "finished outer rule");
        assertEquals(expectedLog, LOG);
    }

    @Test
    public void aroundShouldNotAllowNullRules() {
        RuleChain chain = RuleChain.emptyRuleChain();
        try {
            chain.around(null);
            fail("around() should not allow null rules");
        } catch (NullPointerException e) {
            assertThat(e.getMessage(), equalTo("The enclosed rule must not be null"));
        }
    }

    public static class RuleChainWithNullRules {
        @Rule
        public final RuleChain chain = outerRule(new LoggingRule("outer rule"))
                .around(null);

        @Test
        public void example() {}
    }

    @Test
    public void whenRuleChainHasNullRuleTheStacktraceShouldPointToIt() {
        Result result = JUnitCore.runClasses(RuleChainWithNullRules.class);

        assertThat(result.getFailures().size(), equalTo(1));
        String stacktrace = Throwables.getStacktrace(result.getFailures().get(0).getException());
        assertThat(stacktrace, containsString("\tat org.junit.rules.RuleChainTest$RuleChainWithNullRules.<init>(RuleChainTest.java:"));
    }
}