Update InMemoryRichGaugeRepository to support increments

Closes gh-2902

spring-boot-actuator/src/main/java/org/springframework/boot/actuate/metrics/rich/InMemoryRichGaugeRepository.java

 /*
- * Copyright 2012-2016 the original author or authors.
+ * Copyright 2012-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -24,19 +24,32 @@ import org.springframework.boot.actuate.metrics.writer.MetricWriter;
 
 /**
  * In memory implementation of {@link MetricWriter} and {@link RichGaugeReader}. When you
- * set a metric value (using {@link MetricWriter#set(Metric)}) it is used to update a rich
- * gauge (increment is a no-op). Gauge values can then be read out using the reader
- * operations.
+ * {@link MetricWriter#set(Metric) set} or {@link MetricWriter#increment(Delta) increment}
+ * a metric value it is used to update a {@link RichGauge}. Gauge values can then be read
+ * out using the reader operations.
  *
  * @author Dave Syer
+ * @author Andy Wilkinson
  */
 public class InMemoryRichGaugeRepository implements RichGaugeRepository {
 
 	private final SimpleInMemoryRepository<RichGauge> repository = new SimpleInMemoryRepository<RichGauge>();
 
 	@Override
-	public void increment(Delta<?> delta) {
-		// No-op
+	public void increment(final Delta<?> delta) {
+		this.repository.update(delta.getName(), new Callback<RichGauge>() {
+
+			@Override
+			public RichGauge modify(RichGauge current) {
+				double value = ((Number) delta.getValue()).doubleValue();
+				if (current == null) {
+					return new RichGauge(delta.getName(), value);
+				}
+				current.set(current.getValue() + value);
+				return current;
+			}
+
+		});
 	}
 
 	@Override

spring-boot-actuator/src/test/java/org/springframework/boot/actuate/metrics/rich/InMemoryRichGaugeRepositoryTests.java

 /*
- * Copyright 2012-2016 the original author or authors.
+ * Copyright 2012-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -19,12 +19,16 @@ package org.springframework.boot.actuate.metrics.rich;
 import org.junit.Test;
 
 import org.springframework.boot.actuate.metrics.Metric;
+import org.springframework.boot.actuate.metrics.writer.Delta;
 
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.offset;
 
 /**
+ * Tests for {@link InMemoryRichGaugeRepository}.
+ *
  * @author Dave Syer
+ * @author Andy Wilkinson
  */
 public class InMemoryRichGaugeRepositoryTests {
 
@@ -38,4 +42,19 @@ public class InMemoryRichGaugeRepositoryTests {
 		assertThat(this.repository.findOne("foo").getValue()).isEqualTo(2d, offset(0.01));
 	}
 
+	@Test
+	public void incrementExisting() {
+		this.repository.set(new Metric<Double>("foo", 1d));
+		this.repository.increment(new Delta<Double>("foo", 2d));
+		assertThat(this.repository.findOne("foo").getCount()).isEqualTo(2L);
+		assertThat(this.repository.findOne("foo").getValue()).isEqualTo(3d, offset(0.01));
+	}
+
+	@Test
+	public void incrementNew() {
+		this.repository.increment(new Delta<Double>("foo", 2d));
+		assertThat(this.repository.findOne("foo").getCount()).isEqualTo(1L);
+		assertThat(this.repository.findOne("foo").getValue()).isEqualTo(2d, offset(0.01));
+	}
+
 }