add unit test for plain text scenarios

Author: sagnghos

google-cloud-spanner/src/main/java/com/google/cloud/spanner/SpannerOptions.java

@@ -1631,6 +1631,7 @@ public Builder usePlainText() {
         this.experimentalHost = "http://" + this.experimentalHost;
         super.setHost(this.experimentalHost);
       }
+      this.usePlainText = true;
       return this;
     }
 

google-cloud-spanner/src/test/java/com/google/cloud/spanner/SpannerOptionsTest.java

@@ -1199,4 +1199,27 @@ public void testExperimentalHostOptions() {
     assertTrue(options.getSessionPoolOptions().getUseMultiplexedSessionForRW());
     assertTrue(options.getSessionPoolOptions().getUseMultiplexedSessionPartitionedOps());
   }
+
+  @Test
+  public void testPlainTextOptions() {
+    SpannerOptions options =
+        SpannerOptions.newBuilder().setExperimentalHost("localhost:8080").usePlainText().build();
+    assertEquals("http://localhost:8080", options.getHost());
+    assertEquals(NoCredentials.getInstance(), options.getCredentials());
+    options =
+        SpannerOptions.newBuilder()
+            .setExperimentalHost("http://localhost:8080")
+            .usePlainText()
+            .build();
+    assertEquals("http://localhost:8080", options.getHost());
+    options =
+        SpannerOptions.newBuilder().usePlainText().setExperimentalHost("localhost:8080").build();
+    assertEquals("http://localhost:8080", options.getHost());
+    options =
+        SpannerOptions.newBuilder()
+            .usePlainText()
+            .setExperimentalHost("http://localhost:8080")
+            .build();
+    assertEquals("http://localhost:8080", options.getHost());
+  }
 }