feat(block-kit): add alert block example

block-kit/README.md

@@ -9,6 +9,7 @@ Read the [docs](https://docs.slack.dev/block-kit/) to learn concepts behind thes
 ### Blocks
 
 - **[Actions](https://docs.slack.dev/reference/block-kit/blocks/actions-block)**: Holds multiple interactive elements. [Implementation](./src/main/java/blocks/Actions.java).
+- **[Alert](https://docs.slack.dev/reference/block-kit/blocks/alert-block)**: Displays alerts, warnings, and informational messages. [Implementation](./src/main/java/blocks/Alert.java).
 - **[Carousel](https://docs.slack.dev/reference/block-kit/blocks/carousel-block)**: Displays related card blocks in a horizontally-scrolling container. [Implementation](./src/main/java/blocks/Carousel.java).
 - **[Card](https://docs.slack.dev/reference/block-kit/blocks/card-block)**: Displays content in a card. [Implementation](./src/main/java/blocks/Card.java).
 - **[Context](https://docs.slack.dev/reference/block-kit/blocks/context-block)**: Provides contextual info, which can include both images and text. [Implementation](./src/main/java/blocks/Context.java).

block-kit/src/main/java/blocks/Alert.java

@@ -0,0 +1,21 @@
+package blocks;
+
+import com.slack.api.model.block.AlertBlock;
+import com.slack.api.model.block.Blocks;
+import com.slack.api.model.block.composition.BlockCompositions;
+
+/**
+ * Displays alerts, warnings, and informational messages.
+ * {@link https://docs.slack.dev/reference/block-kit/blocks/alert-block/}
+ */
+public class Alert {
+    /**
+     * An informational alert block.
+     */
+    public static AlertBlock example01() {
+        AlertBlock block =
+                Blocks.alert(a -> a.text(BlockCompositions.markdownText("The work is mysterious and important."))
+                        .level("info"));
+        return block;
+    }
+}

block-kit/src/test/java/blocks/AlertTest.java

@@ -0,0 +1,27 @@
+package blocks;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import com.google.gson.JsonParser;
+import com.slack.api.model.block.AlertBlock;
+import com.slack.api.util.json.GsonFactory;
+import org.junit.jupiter.api.Test;
+
+public class AlertTest {
+    @Test
+    public void testExample01() {
+        AlertBlock block = Alert.example01();
+        String actual = GsonFactory.createSnakeCase().toJson(block);
+        String expected = """
+            {
+              "type": "alert",
+              "text": {
+                "type": "mrkdwn",
+                "text": "The work is mysterious and important."
+              },
+              "level": "info"
+            }
+            """;
+        assertEquals(JsonParser.parseString(expected), JsonParser.parseString(actual));
+    }
+}