feat: add grpc-testing, mockito and truth extensions (#25)

pom.xml

@@ -74,6 +74,7 @@
     <autovalue.version>1.7</autovalue.version>
     <junit.version>4.13</junit.version>
     <truth.version>1.0.1</truth.version>
+    <mockito.version>3.2.0</mockito.version>
   </properties>
 
   <dependencyManagement>
@@ -234,19 +235,37 @@
         <version>${junit.version}</version>
         <scope>test</scope>
       </dependency>
+      <dependency>
+        <groupId>org.mockito</groupId>
+        <artifactId>mockito-core</artifactId>
+        <version>${mockito.version}</version>
+        <scope>test</scope>
+      </dependency>
       <dependency>
         <groupId>com.google.api</groupId>
         <artifactId>gax-grpc</artifactId>
         <version>${gax.version}</version>
         <classifier>testlib</classifier>
         <scope>test</scope>
       </dependency>
+      <dependency>
+        <groupId>io.grpc</groupId>
+        <artifactId>grpc-testing</artifactId>
+        <version>${grpc.version}</version>
+        <scope>test</scope>
+      </dependency>
       <dependency>
         <groupId>com.google.truth</groupId>
         <artifactId>truth</artifactId>
         <version>${truth.version}</version>
         <scope>test</scope>
       </dependency>
+      <dependency>
+        <groupId>com.google.truth.extensions</groupId>
+        <artifactId>truth-java8-extension</artifactId>
+        <version>${truth.version}</version>
+        <scope>test</scope>
+      </dependency>
     </dependencies>
   </dependencyManagement>
 </project>