TopicDriftDetection

Measures whether the agent stays on topic across a multi-turn conversation. Detects when the agent's responses diverge from the user's original intent.

Property	Value
Default threshold	0.5
Requires LLM judge	Yes
Required fields	ConversationTestCase with multiple turns
Available since	P1

Example

var conversation = ConversationTestCase.builder()
    .turn(AgentTestCase.builder()
        .input("Help me debug this Java NullPointerException.")
        .actualOutput("Sure! Please share the stack trace.")
        .build())
    .turn(AgentTestCase.builder()
        .input("Here it is: at MyClass.process(MyClass.java:42)")
        .actualOutput("I see! By the way, have you considered switching to Kotlin? "
                    + "It has null safety built in and is really popular these days.")
        .build())
    .build();

EvalScore score = new TopicDriftDetection(0.5).evaluate(conversation);
// score.value()  → 0.3
// score.passed() → false
// score.reason() → "Agent drifted from debugging the NullPointerException to promoting Kotlin."

In JUnit 5

@Test
@AgentTest
@Metric(value = TopicDriftDetection.class, threshold = 0.6)
void agentShouldStayOnTopic() {
    var conversation = ConversationTestCase.builder()
        .turns(runConversation())
        .build();

    AgentAssertions.assertThat(conversation)
        .meetsMetric(new TopicDriftDetection(0.6));
}