我刚刚发现在hadoop 2.x中，没有hadoop核心，所以正确的pom是：

<dependency>
    <groupId>org.apache.hadoop</groupId>
    <artifactId>hadoop-common</artifactId>
    <version>2.9.0</version>
    <scope>provided</scope>
</dependency>
<dependency>
    <groupId>org.apache.hadoop</groupId>
    <artifactId>hadoop-mapreduce-client-core</artifactId>
    <version>2.9.0</version>
</dependency>
<dependency>
    <groupId>org.apache.hadoop</groupId>
    <artifactId>hadoop-hdfs</artifactId>
    <version>2.9.0</version>
</dependency>
<dependency>
    <groupId>org.apache.mrunit</groupId>
    <artifactId>mrunit</artifactId>
    <version>1.1.0</version>
    <classifier>hadoop2</classifier>
    <scope>test</scope>
</dependency>

尝试添加不同的jar版本。
我从 mrunit-1.1.0.jar 至 mrunit-0.9.0-incubating-hadoop2.jar 旧的jar:- public interface Mapper<K1, V1, K2, V2> extends JobConfigurable, Closeable { } 新建jar:-

public class Mapper<KEYIN, VALUEIN, KEYOUT, VALUEOUT> {}

我刚刚将jar从hadoop1改为hadoop2，然后我的所有单元测试用例都成功运行了。https://issues.apache.org/jira/browse/mrunit-156

<project xmlns="http://maven.apache.org/POM/4.0.0"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>com.org</groupId>
    <artifactId>com.org</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <dependencies>
        <!-- JDK Tools -->
        <dependency>
            <groupId>jdk.tools</groupId>
            <artifactId>jdk.tools</artifactId>
            <scope>system</scope>
            <version>1.8.0_73</version>
            <systemPath>${JAVA_HOME}/lib/tools.jar</systemPath>
        </dependency>
        <!-- Hadoop Core -->
        <dependency>
            <groupId>org.apache.hadoop</groupId>
            <artifactId>hadoop-core</artifactId>
            <version>1.2.1</version>
        </dependency>
        <!-- Hadoop Mapreduce Client Core -->
        <dependency>
            <groupId>org.apache.hadoop</groupId>
            <artifactId>hadoop-mapreduce-client-core</artifactId>
            <version>2.7.1</version>
        </dependency>

        <dependency>
            <groupId>org.apache.mrunit</groupId>
            <artifactId>mrunit</artifactId>
            <version>0.9.0-incubating</version>
            <classifier>hadoop1</classifier>
        </dependency>
        <dependency>
            <groupId>org.apache.mrunit</groupId>
            <artifactId>mrunit</artifactId>
            <version>0.9.0-incubating</version>
            <classifier>hadoop2</classifier>
        </dependency>

    </dependencies>

</project>