public boolean isMissing() {
        return cachedFile == null;
    }

    @Override
    public File getCachedFile() {
        return cachedFile;
    }

    @Override
    public long getCachedAt() {
        return cachedAt;
    }

    @Override
    public ExternalResourceMetaData getExternalResourceMetaData() {
        return externalResourceMetaData;
    }

    @Override

     */
    @Nullable
    File getCachedFile();

    /**
     * The timestamp of when this cache entry was created.
     *
     * @return The timestamp of when this cache entry was created.
     */
    long getCachedAt();

    public boolean isMissing() {
        return cachedFile == null;
    }

    @Override
    public File getCachedFile() {
        return cachedFile;
    }

    @Override
    public long getCachedAt() {
        return cachedAt;
    }

    @Override
    public HashCode getDescriptorHash() {
        return descriptorHash;
    }

    @Override
    public List<String> attemptedLocations() {

                return missing
            }

            @Override
            File getCachedFile() {
                return file
            }

            @Override
            long getCachedAt() {
                return 0
            }
        }
    }

            if (value.getCachedFile() != null) {
                encoder.writeString(relativizeAndNormalizeFilePath(value.getCachedFile()));
            }
            encoder.writeLong(value.getCachedAt());
            ExternalResourceMetaData metaData = value.getExternalResourceMetaData();
            encoder.writeBoolean(metaData != null);
            if (metaData != null) {

        }

        @Override
        public void write(Encoder encoder, CachedArtifact value) throws Exception {
            encoder.writeBoolean(value.isMissing());
            encoder.writeLong(value.getCachedAt());
            byte[] hash = value.getDescriptorHash().toByteArray();
            encoder.writeBinary(hash);
            if (!value.isMissing()) {

        });
    }

    private long getAgeMillis(BuildCommencedTimeProvider timeProvider, CachedExternalResource cached) {
        return timeProvider.getCurrentTime() - cached.getCachedAt();
    }

        then:
        result == resultResource

        and:
        1 * index.lookup("thing") >> Stub(CachedExternalResource) {
            getCachedAt() >> 23999L
            getExternalResourceMetaData() >> cachedMetaData
            getCachedFile() >> cachedFile
        }
        timeProvider.currentTime >> 24000L

                final HashCode descriptorHash = moduleSource.getDescriptorHash();
                Duration age = Duration.ofMillis(timeProvider.getCurrentTime() - cached.getCachedAt());
                final boolean isChangingModule = moduleSource.isChangingModule();
                ModuleComponentArtifactMetadata moduleComponentArtifactMetadata = (ModuleComponentArtifactMetadata) artifact;