The test in test/langtools/tools/javac/T8187978 tests that javac emits proper diagnostics when overload method resolution fails for the code being compiled. It uses a reference file ("golden file") technique to verify correct operation.

Unfortunately, the reference file includes information about actual methods in java.util.ArrayList, including the following:

public boolean add(E)
public void add(int, E)
private void add(E, Object[], int)

The first two methods are methods in the public API and are unlikely ever to change. However, the third method is a private method, and changing it causes the test to fail. This can be illustrated by applying this patch:

diff --git a/src/java.base/share/classes/java/util/ArrayList.java b/src/java.base/share/classes/java/util/ArrayList.java
index a36dcd8a796..8cac9e72afa 100644
--- a/src/java.base/share/classes/java/util/ArrayList.java
+++ b/src/java.base/share/classes/java/util/ArrayList.java
@@ -449,7 +449,7 @@ public class ArrayList<E> extends AbstractList<E>
      * bytecode size under 35 (the -XX:MaxInlineSize default value),
      * which helps when add(E) is called in a C1-compiled loop.
      */
- private void add(E e, Object[] elementData, int s) {
+ private void addx(E e, Object[] elementData, int s) {
         if (s == elementData.length)
             elementData = grow();
         elementData[s] = e;
@@ -464,7 +464,7 @@ public class ArrayList<E> extends AbstractList<E>
      */
     public boolean add(E e) {
         modCount++;
- add(e, elementData, size);
+ addx(e, elementData, size);
         return true;
     }