[GitHub] [pulsar] Jennifer88huang commented on a change in pull request #4485: add docs on how to debug Pulsar Functions

[GitBox <gi...@apache.org>]

Jennifer88huang commented on a change in pull request #4485: add docs on how to debug Pulsar Functions
URL: https://github.com/apache/pulsar/pull/4485#discussion_r291824705
 
 

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 File path: site2/docs/functions-debugging.md
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 @@ -0,0 +1,121 @@
+---
+id: functions-debugging
+title: Debugging Pulsar Functions
+sidebar_label: Debugging functions
+---
+
+A Pulsar Function at its core is just a function with inputs and outputs, thus testing a Pulsar Function can be done in a similar way as testing any function.
+
+For example, if a user has the following Pulsar Function:
+
+```java
+import java.util.function.Function;
+
+public class JavaNativeExclamationFunction implements Function<String, String> {
+   @Override
+   public String apply(String input) {
+       return String.format("%s!", input);
+   }
+}
+```
+
+The user can write a simple unit test to test this Pulsar function:
+
+```java
+@Test
+public void testJavaNativeExclamationFunction() {
+   JavaNativeExclamationFunction exclamation = new JavaNativeExclamationFunction();
+   String output = exclamation.apply("foo");
+   Assert.assertEquals(output, "foo!");
+}
+```
+
+Consequently, if a user has a Pulsar Function that implements the ```org.apache.pulsar.functions.api.Function``` interface:
+
+```java
+import org.apache.pulsar.functions.api.Context;
+import org.apache.pulsar.functions.api.Function;
+
+public class ExclamationFunction implements Function<String, String> {
+   @Override
+   public String process(String input, Context context) {
+       return String.format("%s!", input);
+   }
+}
+```
+
+The user can write a unit test for this function as well. Just be remember to mock out the ```Context``` parameter.
+
+For example:
+
+```java
+@Test
+public void testExclamationFunction() {
+   ExclamationFunction exclamation = new ExclamationFunction();
+   String output = exclamation.process("foo", mock(Context.class));
+   Assert.assertEquals(output, "foo!");
+}
+```
+
+## Debugging with localrun mode
 
 Review comment:
   ```suggestion
   ## Debug with the localrun mode
   ```

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