1655112 - Unintuitive error message when testGetValue does not have a value

Status: RESOLVED FIXED

(Data Platform and Tools :: Glean: SDK, defect, P2)

Description

[Michael Comella (:mcomella) [NI reported issues only: ex-Mozilla]]

Attachment: thrown-exception.txt

Example code:

@Test
fun showErrorMessage() {
    org.mozilla.fenix.GleanMetrics.StorageStats.appBytes.testGetValue()
}

This will throw an error (full trace attached):

java.lang.NullPointerException
	at mozilla.telemetry.glean.private.MemoryDistributionMetricType.testGetValue(MemoryDistributionMetricType.kt:128)
	at mozilla.telemetry.glean.private.MemoryDistributionMetricType.testGetValue$default(MemoryDistributionMetricType.kt:123)
...

Usually, a NullPointerException implies programmer error so I interpret this error to mean either:

• I messed up by using a null reference
• There's a bug in a library for that reason

However, the real issue is that there is no value set in StorageStats.appBytes and it requires a little debugging to realize that (I had to look at the glean source to figure it out).

I think it would be more intuitive to do one of, in order of preference:

• throw a custom exception (GleanTestException?) with a message like, "metric must have value set if testGetValue is called. See testHasValue to check for existence"
• throw an IllegalStateException (which is more intuitive than NPE) with a similar message
• Add a similar message to the existing NullPointerException

Comment 1

[Michael Comella (:mcomella) [NI reported issues only: ex-Mozilla]]

This occurred again and prompted me to want to file another issue: https://github.com/mozilla-mobile/fenix/issues/17725#issuecomment-771070137

Comment 2

[GitHub Bugzilla PR Linker]

Attachment: Link to GitHub pull-request: https://github.com/mozilla/glean/pull/1491