Isolated execution of MapperFootprintTest (#3678)

Author: yawkat

pom.xml

@@ -181,13 +181,37 @@
         <groupId>org.apache.maven.plugins</groupId>
         <version>${version.plugin.surefire}</version>
         <artifactId>maven-surefire-plugin</artifactId>
+        <executions>
+          <execution>
+            <id>default-test</id>
+            <goals>
+              <goal>test</goal>
+            </goals>
+            <phase>test</phase>
+            <configuration>
+              <excludes>
+                <exclude>com.fasterxml.jackson.databind.MapperFootprintTest</exclude>
+                <exclude>**/failing/**/*.java</exclude>
+              </excludes>
+            </configuration>
+          </execution>
+          <execution>
+            <id>footprint-test</id>
+            <goals>
+              <goal>test</goal>
+            </goals>
+            <phase>test</phase>
+            <configuration>
+              <includes>
+                <include>com.fasterxml.jackson.databind.MapperFootprintTest</include>
+              </includes>
+            </configuration>
+          </execution>
+        </executions>
         <configuration>
           <classpathDependencyExcludes>
             <exclude>javax.measure:jsr-275</exclude>
           </classpathDependencyExcludes>
-          <excludes>
-            <exclude>**/failing/**/*.java</exclude>
-          </excludes>
           <!-- 26-Nov-2019, tatu: moar parallelism! Per-class basis, safe, efficient enough
                   ... although not 100% sure this makes much difference TBH
             -->

src/test/java/com/fasterxml/jackson/databind/MapperFootprintTest.java

@@ -2,13 +2,16 @@
 
 import com.google.common.testing.GcFinalization;
 import org.junit.Assert;
-import org.junit.Ignore;
 import org.junit.Test;
 import org.openjdk.jol.info.GraphLayout;
 
 public class MapperFootprintTest {
+    /*
+     * Note: this class is run in an isolated execution in surefire. The test is too flaky with all the other tests
+     * running in the same JVM.
+     */
+
     @Test
-    @Ignore
     public void testMapperFootprint() throws InterruptedException {
         // memory footprint limit for the ObjectMapper