Add parent Observation to the toString() of Observation.Context

fixes gh-3542

Author: jonatan-ivanov

micrometer-observation/src/main/java/io/micrometer/observation/Observation.java

@@ -1042,8 +1042,8 @@ public KeyValues getAllKeyValues() {
         public String toString() {
             return "name='" + name + '\'' + ", contextualName='" + contextualName + '\'' + ", error='" + error + '\''
                     + ", lowCardinalityKeyValues=" + toString(getLowCardinalityKeyValues())
-                    + ", highCardinalityKeyValues=" + toString(getHighCardinalityKeyValues()) + ", map="
-                    + toString(map);
+                    + ", highCardinalityKeyValues=" + toString(getHighCardinalityKeyValues()) + ", map=" + toString(map)
+                    + ", parentObservation=" + parentObservation;
         }
 
         private String toString(KeyValues keyValues) {

micrometer-observation/src/test/java/io/micrometer/observation/ObservationTextPublisherTests.java

@@ -30,7 +30,7 @@
  */
 class ObservationTextPublisherTests {
 
-    private static final String CONTEXT_TOSTRING = "name='testName', contextualName='testContextualName', error='java.io.IOException: simulated', lowCardinalityKeyValues=[lcTag='foo'], highCardinalityKeyValues=[hcTag='bar'], map=[contextKey='contextValue']";
+    private static final String CONTEXT_TOSTRING = "name='testName', contextualName='testContextualName', error='java.io.IOException: simulated', lowCardinalityKeyValues=[lcTag='foo'], highCardinalityKeyValues=[hcTag='bar'], map=[contextKey='contextValue'], parentObservation=null";
 
     private final TestConsumer consumer = new TestConsumer();