Add support for AssertJ

Add AssertJ as a managed dependency and also include it in
spring-boot-starter-test. Also provide a simple adapter class to allow
Hamcrest matchers to be used as AssertJ Conditions.

Fixes gh-5048

spring-boot-dependencies/pom.xml

@@ -47,6 +47,7 @@
 		<antlr2.version>2.7.7</antlr2.version>
 		<artemis.version>1.1.0</artemis.version>
 		<aspectj.version>1.8.8</aspectj.version>
+		<assertj.version>2.3.0</assertj.version>
 		<atomikos.version>3.9.3</atomikos.version>
 		<bitronix.version>2.1.4</bitronix.version>
 		<cassandra-driver.version>2.1.9</cassandra-driver.version>
@@ -1173,6 +1174,11 @@
 				<artifactId>aspectjweaver</artifactId>
 				<version>${aspectj.version}</version>
 			</dependency>
+			<dependency>
+				<groupId>org.assertj</groupId>
+				<artifactId>assertj-core</artifactId>
+				<version>${assertj.version}</version>
+			</dependency>
 			<dependency>
 				<groupId>org.codehaus.btm</groupId>
 				<artifactId>btm</artifactId>

spring-boot-docs/pom.xml

@@ -125,6 +125,11 @@
 			<artifactId>commons-pool2</artifactId>
 			<optional>true</optional>
 		</dependency>
+		<dependency>
+			<groupId>org.assertj</groupId>
+			<artifactId>assertj-core</artifactId>
+			<optional>true</optional>
+		</dependency>
 		<dependency>
 			<groupId>io.dropwizard.metrics</groupId>
 			<artifactId>metrics-core</artifactId>

spring-boot-parent/pom.xml

@@ -211,6 +211,11 @@
 			<artifactId>junit</artifactId>
 			<scope>test</scope>
 		</dependency>
+		<dependency>
+			<groupId>org.assertj</groupId>
+			<artifactId>assertj-core</artifactId>
+			<scope>test</scope>
+		</dependency>
 		<dependency>
 			<groupId>org.mockito</groupId>
 			<artifactId>mockito-core</artifactId>

spring-boot-starters/spring-boot-starter-test/pom.xml

@@ -22,6 +22,10 @@
 			<groupId>junit</groupId>
 			<artifactId>junit</artifactId>
 		</dependency>
+		<dependency>
+			<groupId>org.assertj</groupId>
+			<artifactId>assertj-core</artifactId>
+		</dependency>
 		<dependency>
 			<groupId>org.mockito</groupId>
 			<artifactId>mockito-core</artifactId>

spring-boot/pom.xml

@@ -124,6 +124,11 @@
 			<artifactId>velocity-tools</artifactId>
 			<optional>true</optional>
 		</dependency>
+		<dependency>
+			<groupId>org.assertj</groupId>
+			<artifactId>assertj-core</artifactId>
+			<optional>true</optional>
+		</dependency>
 		<dependency>
 			<groupId>org.codehaus.btm</groupId>
 			<artifactId>btm</artifactId>

spring-boot/src/main/java/org/springframework/boot/test/assertj/Matched.java

@@ -0,0 +1,67 @@
+/*
+ * Copyright 2012-2015 the original author or authors.
+ *
+ * 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 org.springframework.boot.test.assertj;
+
+import org.assertj.core.api.Condition;
+import org.hamcrest.Matcher;
+import org.hamcrest.StringDescription;
+
+import org.springframework.util.Assert;
+
+/**
+ * Adapter class allowing a Hamcrest {@link Matcher} to be used as an AssertJ
+ * {@link Condition}.
+ * <p>
+ * Usually used with the {@code is} method of {@code assertThat}, for example:
+ *
+ * <pre class="code">
+ * assertThat("1234").is(Matched.when(startsWith("12")));
+ * </pre>
+ *
+ * @param <T> The type of object that the condition accepts
+ * @author Phillip Webb
+ * @since 1.4
+ */
+public final class Matched<T> extends Condition<T> {
+
+	private final Matcher<? extends T> matcher;
+
+	private Matched(Matcher<? extends T> matcher) {
+		Assert.notNull(matcher, "Matcher must not be null");
+		this.matcher = matcher;
+	}
+
+	@Override
+	public boolean matches(final T value) {
+		if (this.matcher.matches(value)) {
+			return true;
+		}
+		StringDescription description = new StringDescription();
+		this.matcher.describeTo(description);
+		describedAs(description.toString());
+		return false;
+	}
+
+	public static <T> Condition<T> when(Matcher<? extends T> matcher) {
+		return by(matcher);
+	}
+
+	public static <T> Condition<T> by(Matcher<? extends T> matcher) {
+		return new Matched<T>(matcher);
+	}
+
+}

spring-boot/src/test/java/org/springframework/boot/test/assertj/MatchedTests.java

@@ -0,0 +1,60 @@
+/*
+ * Copyright 2012-2015 the original author or authors.
+ *
+ * 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 org.springframework.boot.test.assertj;
+
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.ExpectedException;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.hamcrest.Matchers.startsWith;
+
+/**
+ * Tests for {@link Matched}.
+ *
+ * @author Phillip Webb
+ */
+public class MatchedTests {
+
+	@Rule
+	public ExpectedException thrown = ExpectedException.none();
+
+	@Test
+	public void byMatcherMatches() {
+		assertThat("1234").is(Matched.by(startsWith("12")));
+	}
+
+	@Test
+	public void byMatcherDoesNotMatch() {
+		this.thrown.expect(AssertionError.class);
+		this.thrown.expectMessage("a string starting with \"23\"");
+		assertThat("1234").is(Matched.by(startsWith("23")));
+	}
+
+	@Test
+	public void whenMatcherMatches() {
+		assertThat("1234").is(Matched.when(startsWith("12")));
+	}
+
+	@Test
+	public void whenMatcherDoesNotMatch() {
+		this.thrown.expect(AssertionError.class);
+		this.thrown.expectMessage("a string starting with \"23\"");
+		assertThat("1234").is(Matched.when(startsWith("23")));
+	}
+
+}