chore: declare test-jar in GAX's testlib artifacts (#1474)

* chore: add test jar

* add test jar for showcase

* how about duplicating entries?

* testlib for gax-httpjson too

* add source comment

---------

Co-authored-by: Tomo Suzuki <[email protected]>

Author: JoeWang1127

gapic-generator-java/pom.xml

@@ -374,6 +374,8 @@
     <dependency>
       <groupId>com.google.api</groupId>
       <artifactId>gax</artifactId>
+      <!-- import the test code, https://maven.apache.org/plugins/maven-jar-plugin/examples/create-test-jar.html -->
+      <type>test-jar</type>
       <classifier>testlib</classifier>
     </dependency>
     <dependency>
@@ -383,6 +385,8 @@
     <dependency>
       <groupId>com.google.api</groupId>
       <artifactId>gax-grpc</artifactId>
+      <!-- import the test code, https://maven.apache.org/plugins/maven-jar-plugin/examples/create-test-jar.html -->
+      <type>test-jar</type>
       <classifier>testlib</classifier>
     </dependency>
     <dependency>
@@ -392,6 +396,8 @@
     <dependency>
       <groupId>com.google.api</groupId>
       <artifactId>gax-httpjson</artifactId>
+      <!-- import the test code, https://maven.apache.org/plugins/maven-jar-plugin/examples/create-test-jar.html -->
+      <type>test-jar</type>
       <classifier>testlib</classifier>
     </dependency>
     <dependency>

gax-java/gax-bom/pom.xml

@@ -12,6 +12,7 @@
     <groupId>com.google.cloud</groupId>
     <artifactId>google-cloud-shared-config</artifactId>
     <version>1.5.5</version>
+    <relativePath/>
   </parent>
 
   <developers>
@@ -48,12 +49,26 @@
         <groupId>com.google.api</groupId>
         <artifactId>gax</artifactId>
         <version>2.23.3-SNAPSHOT</version><!-- {x-version-update:gax:current} -->
+        <type>test-jar</type>
         <classifier>testlib</classifier>
       </dependency>
+      <dependency>
+        <groupId>com.google.api</groupId>
+        <artifactId>gax</artifactId>
+        <version>2.23.3-SNAPSHOT</version><!-- {x-version-update:gax:current} -->
+        <classifier>testlib</classifier>
+      </dependency>
+      <dependency>
+        <groupId>com.google.api</groupId>
+        <artifactId>gax-grpc</artifactId>
+        <version>2.23.3-SNAPSHOT</version><!-- {x-version-update:gax-grpc:current} -->
+      </dependency>
       <dependency>
         <groupId>com.google.api</groupId>
         <artifactId>gax-grpc</artifactId>
         <version>2.23.3-SNAPSHOT</version><!-- {x-version-update:gax-grpc:current} -->
+        <type>test-jar</type>
+        <classifier>testlib</classifier>
       </dependency>
       <dependency>
         <groupId>com.google.api</groupId>
@@ -66,6 +81,13 @@
         <artifactId>gax-httpjson</artifactId>
         <version>0.108.3-SNAPSHOT</version><!-- {x-version-update:gax-httpjson:current} -->
       </dependency>
+      <dependency>
+        <groupId>com.google.api</groupId>
+        <artifactId>gax-httpjson</artifactId>
+        <version>0.108.3-SNAPSHOT</version><!-- {x-version-update:gax-httpjson:current} -->
+        <type>test-jar</type>
+        <classifier>testlib</classifier>
+      </dependency>
       <dependency>
         <groupId>com.google.api</groupId>
         <artifactId>gax-httpjson</artifactId>