tests: fixes jdbc query options test (#468)

* tests: fixes jdbc query options test

This test was failing, because we were no longer recreating the jdbc
connection from scratch. One of the tests, set an environment variable
specifying the optimizer version, which was permanently applied, since
the connection was not re-created.

Here we make sure to start / stop the static server before each test.

* chore: fixes linting errors

src/test/java/com/google/cloud/spanner/jdbc/JdbcQueryOptionsTest.java

@@ -26,12 +26,19 @@
 import com.google.spanner.v1.ExecuteSqlRequest;
 import java.sql.DriverManager;
 import java.sql.SQLException;
+import org.junit.Before;
 import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.junit.runners.JUnit4;
 
 @RunWith(JUnit4.class)
 public class JdbcQueryOptionsTest extends AbstractMockServerTest {
+  @Before
+  public void setup() throws Exception {
+    stopServer();
+    startStaticServer();
+  }
+
   @Test
   public void testDefaultOptimizerVersion() throws SQLException {
     try (java.sql.Connection connection = createJdbcConnection()) {
@@ -151,13 +158,7 @@ public void testUseOptimizerVersionFromConnectionUrl() throws SQLException {
   @Test
   public void testUseOptimizerVersionFromEnvironment() throws SQLException {
     try {
-      SpannerOptions.useEnvironment(
-          new SpannerOptions.SpannerEnvironment() {
-            @Override
-            public String getOptimizerVersion() {
-              return "20";
-            }
-          });
+      SpannerOptions.useEnvironment(() -> "20");
       try (java.sql.Connection connection =
           DriverManager.getConnection(String.format("jdbc:%s", getBaseUrl()))) {
         // Do a query and verify that the version from the environment is used.