Added tests and changes as requested

Author: speedythesnail

testng-core/src/main/java/org/testng/internal/YamlParser.java

@@ -21,7 +21,7 @@ public XmlSuite parse(String filePath, InputStream is, boolean loadClasses)
 
   @Override
   public boolean accept(String fileName) {
-    return Parser.hasFileScheme(fileName) && fileName.endsWith(".yaml")
-        || fileName.endsWith(".yml");
+    return Parser.hasFileScheme(fileName)
+        && (fileName.endsWith(".yaml") || fileName.endsWith(".yml"));
   }
 }

testng-core/src/test/java/test/yaml/YamlTest.java

@@ -1,6 +1,8 @@
 package test.yaml;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
 
 import java.io.File;
 import java.io.FileInputStream;
@@ -31,6 +33,17 @@ public Object[][] dp() {
     };
   }
 
+  @Test(
+      description =
+          "Validate that the YamlParser accepts yaml files with a .yaml or a .yml file extension, but not other file types.")
+  public void accept() {
+    YamlParser yamlParser = new YamlParser();
+
+    assertTrue(yamlParser.accept("TestSuite.yml"));
+    assertTrue(yamlParser.accept("TestSuite.yaml"));
+    assertFalse(yamlParser.accept("TestSuite.xml"));
+  }
+
   @Test(dataProvider = "dp")
   public void compareFiles(String name) throws IOException {
     Collection<XmlSuite> s1 =