spanner: expand test coverage for getDatabaseClient() (#3686)

This change also adds the jacoco coverage plugin in the spanner pom.xml
and sets jacoco.skip to true to disable it by default. It can be enabled
by passing -Djacoco.skip=false to the mvn command.

Author: nithinsujir

google-cloud-clients/google-cloud-spanner/pom.xml

@@ -18,9 +18,29 @@
   </parent>
   <properties>
     <site.installationModule>google-cloud-spanner</site.installationModule>
+    <jacoco.skip>true</jacoco.skip>
   </properties>
   <build>
     <plugins>
+      <plugin>
+        <groupId>org.jacoco</groupId>
+        <artifactId>jacoco-maven-plugin</artifactId>
+        <version>0.8.2</version>
+        <executions>
+          <execution>
+            <goals>
+              <goal>prepare-agent</goal>
+            </goals>
+          </execution>
+          <execution>
+            <id>report</id>
+            <phase>prepare-package</phase>
+            <goals>
+              <goal>report</goal>
+            </goals>
+          </execution>
+        </executions>
+      </plugin>
       <plugin>
         <groupId>org.apache.maven.plugins</groupId>
         <artifactId>maven-surefire-plugin</artifactId>

google-cloud-clients/google-cloud-spanner/src/test/java/com/google/cloud/spanner/SpannerImplTest.java

@@ -17,9 +17,10 @@
 package com.google.cloud.spanner;
 
 import static com.google.common.truth.Truth.assertThat;
+import static org.junit.Assert.fail;
 
+import com.google.cloud.grpc.GrpcTransportOptions;
 import com.google.cloud.spanner.spi.v1.SpannerRpc;
-
 import java.util.HashMap;
 import java.util.Map;
 import org.junit.Before;
@@ -70,4 +71,49 @@ public void createAndCloseSession() {
     // The same channelHint is passed for deleteSession (contained in "options").
     Mockito.verify(rpc).deleteSession(sessionName, options.getValue());
   }
+
+  @Test
+  public void getDbclientAgainGivesSame() {
+    Map<String, String> labels = new HashMap<>();
+    labels.put("env", "dev");
+    Mockito.when(spannerOptions.getSessionLabels()).thenReturn(labels);
+    String dbName = "projects/p1/instances/i1/databases/d1";
+    DatabaseId db = DatabaseId.of(dbName);
+
+    Mockito.when(spannerOptions.getTransportOptions())
+        .thenReturn(GrpcTransportOptions.newBuilder().build());
+    Mockito.when(spannerOptions.getSessionPoolOptions())
+        .thenReturn(SessionPoolOptions.newBuilder().build());
+
+    DatabaseClient databaseClient = impl.getDatabaseClient(db);
+
+    // Get db client again
+    DatabaseClient databaseClient1 = impl.getDatabaseClient(db);
+
+    assertThat(databaseClient1).isSameAs(databaseClient);
+  }
+
+  @Test
+  public void getDbclientAfterCloseThrows() {
+    SpannerImpl imp = new SpannerImpl(rpc, 1, spannerOptions);
+    Map<String, String> labels = new HashMap<>();
+    labels.put("env", "dev");
+    Mockito.when(spannerOptions.getSessionLabels()).thenReturn(labels);
+    String dbName = "projects/p1/instances/i1/databases/d1";
+    DatabaseId db = DatabaseId.of(dbName);
+
+    Mockito.when(spannerOptions.getTransportOptions())
+        .thenReturn(GrpcTransportOptions.newBuilder().build());
+    Mockito.when(spannerOptions.getSessionPoolOptions())
+        .thenReturn(SessionPoolOptions.newBuilder().build());
+
+    imp.close();
+
+    try {
+      imp.getDatabaseClient(db);
+      fail("Expected exception");
+    } catch (IllegalStateException e) {
+      assertThat(e.getMessage()).contains("Cloud Spanner client has been closed");
+    }
+  }
 }