check versions.yml for correct project version (#5882)

- and fix a test

logstash-core/build.gradle

@@ -1,17 +1,30 @@
 import java.nio.file.Files
+import org.yaml.snakeyaml.Yaml
 import static java.nio.file.StandardCopyOption.REPLACE_EXISTING
 
 apply plugin: 'java'
 apply plugin: 'idea'
 
 group = 'org.logstash'
-version = '6.0.0-alpha1'
-
 description = """Logstash Core Java"""
 
 sourceCompatibility = 1.8
 targetCompatibility = 1.8
 
+// fetch version from Logstash's master versions.yml file
+def versionMap = (Map) (new Yaml()).load(new File("$projectDir/../versions.yml").text)
+version = versionMap['logstash-core']
+
+buildscript {
+    repositories {
+        mavenCentral()
+    }
+
+    dependencies {
+        classpath 'org.yaml:snakeyaml:1.17'
+    }
+}
+
 configurations {
   provided
 }

logstash-core/src/test/java/org/logstash/log/CustomLogEventTests.java

@@ -33,6 +33,7 @@ import java.util.List;
 import java.util.Map;
 
 import static junit.framework.TestCase.assertEquals;
+import static junit.framework.TestCase.assertNotNull;
 
 public class CustomLogEventTests {
     private static final ObjectMapper mapper = new ObjectMapper();
@@ -78,7 +79,7 @@ public class CustomLogEventTests {
         assertEquals(5, firstMessage.size());
         assertEquals("INFO", firstMessage.get("level"));
         assertEquals("JSONEventLogger", firstMessage.get("loggerName"));
-        assertEquals("main", firstMessage.get("thread"));
+        assertNotNull(firstMessage.get("thread"));
         assertEquals(Collections.singletonMap("message", "simple message"), firstMessage.get("logEvent"));
 
         Map<String, Object> secondMessage = mapper.readValue(messages.get(1), Map.class);
@@ -86,7 +87,7 @@ public class CustomLogEventTests {
         assertEquals(5, secondMessage.size());
         assertEquals("WARN", secondMessage.get("level"));
         assertEquals("JSONEventLogger", secondMessage.get("loggerName"));
-        assertEquals("main", secondMessage.get("thread"));
+        assertNotNull(secondMessage.get("thread"));
         Map<String, Object> logEvent = new HashMap<>();
         logEvent.put("message", "complex message");
         logEvent.put("foo", "bar");