Introduce TestData#delete to simplify testing of flag deletion.

src/main/java/com/launchdarkly/sdk/server/integrations/TestData.java

@@ -110,7 +110,36 @@ public FlagBuilder flag(String key) {
     }
     return new FlagBuilder(key).booleanFlag();
   }
-
+
+  /**
+   * Deletes a specific flag from the test data by create a versioned tombstone.
+   * <p>
+   * This has the same effect as if a flag were removed on the LaunchDarkly dashboard.
+   * It immediately propagates the flag change to any {@code LDClient} instance(s) that you have
+   * already configured to use this {@code TestData}. If no {@code LDClient} has been started yet,
+   * it simply adds tombstone to the test data which will be provided to any {@code LDClient} that
+   * you subsequently configure.
+   *
+   * @param key the flag key
+   * @return a flag configuration builder
+   */
+  public TestData delete(String key) {
+    final ItemDescriptor tombstoneItem;
+    synchronized (lock) {
+      final ItemDescriptor oldItem = currentFlags.get(key);
+      final int oldVersion = oldItem == null ? 0 : oldItem.getVersion();
+      tombstoneItem = ItemDescriptor.deletedItem(oldVersion + 1);
+      currentFlags.put(key, tombstoneItem);
+      currentBuilders.remove(key);
+    }
+
+    for (DataSourceImpl instance: instances) {
+      instance.updates.upsert(DataModel.FEATURES, key, tombstoneItem);
+    }
+
+    return this;
+  }
+
   /**
    * Updates the test data with the specified flag configuration.
    * <p>
@@ -146,7 +175,7 @@ public TestData update(FlagBuilder flagBuilder) {
 
     return this;
   }
-  
+
   /**
    * Simulates a change in the data source status.
    * <p>

src/test/java/com/launchdarkly/sdk/server/integrations/TestDataTest.java

@@ -33,6 +33,7 @@
 import static org.hamcrest.Matchers.is;
 import static org.hamcrest.Matchers.iterableWithSize;
 import static org.hamcrest.Matchers.not;
+import static org.hamcrest.Matchers.notNullValue;
 import static org.hamcrest.Matchers.nullValue;
 
 @SuppressWarnings("javadoc")
@@ -151,7 +152,34 @@ public void updatesFlag() throws Exception {
     expectedFlag.on(true).version(2);
     assertJsonEquals(flagJson(expectedFlag, 2), flagJson(flag1));
   }
-
+
+  @Test
+  public void deletesFlag() throws Exception {
+    final TestData td = TestData.dataSource();
+
+    try (final DataSource ds = td.build(clientContext("", new LDConfig.Builder().build(), updates))) {
+      final Future<Void> started = ds.start();
+      assertThat(started.isDone(), is(true));
+      assertThat(updates.valid, is(true));
+
+      td.update(td.flag("foo").on(false).valueForAll(LDValue.of("bar")));
+      td.delete("foo");
+
+      assertThat(updates.upserts.size(), equalTo(2));
+      UpsertParams up = updates.upserts.take();
+      assertThat(up.kind, is(DataModel.FEATURES));
+      assertThat(up.key, equalTo("foo"));
+      assertThat(up.item.getVersion(), equalTo(1));
+      assertThat(up.item.getItem(), notNullValue());
+
+      up = updates.upserts.take();
+      assertThat(up.kind, is(DataModel.FEATURES));
+      assertThat(up.key, equalTo("foo"));
+      assertThat(up.item.getVersion(), equalTo(2));
+      assertThat(up.item.getItem(), nullValue());
+    }
+  }
+
   @Test
   public void flagConfigSimpleBoolean() throws Exception {
     Function<ModelBuilders.FlagBuilder, ModelBuilders.FlagBuilder> expectedBooleanFlag = fb ->

src/test/java/com/launchdarkly/sdk/server/integrations/TestDataWithClientTest.java

@@ -1,5 +1,7 @@
 package com.launchdarkly.sdk.server.integrations;
 
+import com.launchdarkly.sdk.EvaluationDetail;
+import com.launchdarkly.sdk.EvaluationReason;
 import com.launchdarkly.sdk.LDContext;
 import com.launchdarkly.sdk.LDValue;
 import com.launchdarkly.sdk.server.Components;
@@ -52,7 +54,23 @@ public void updatesFlag() throws Exception {
       assertThat(client.boolVariation("flag", LDContext.create("user"), false), is(true));
     }
   }
-
+
+  @Test
+  public void deletesFlag() throws Exception {
+    td.update(td.flag("flag").on(true));
+
+    try (LDClient client = new LDClient(SDK_KEY, config)) {
+      assertThat(client.boolVariation("flag", LDContext.create("user"), false), is(true));
+
+      td.delete("flag");
+
+      final EvaluationDetail<Boolean> detail = client.boolVariationDetail("flag", LDContext.create("user"), false);
+      assertThat(detail.getValue(), is(false));
+      assertThat(detail.isDefaultValue(), is(true));
+      assertThat(detail.getReason().getErrorKind(), is(EvaluationReason.ErrorKind.FLAG_NOT_FOUND));
+    }
+  }
+
   @Test
   public void usesTargets() throws Exception {
     td.update(td.flag("flag").fallthroughVariation(false).variationForUser("user1", true));