I can not reproduce the issue. Please provide a stack trace and the name of test that cause the error.

Language::getNamespaces() seems to be summing array which does not work whenever one of the operand is null instead of an empty array.

Code is:

$this->namespaceNames = self::$dataCache->getItem( $this->mCode, 'namespaceNames' );
$validNamespaces = MWNamespace::getCanonicalNamespaces();
$this->namespaceNames = $wgExtraNamespaces + $this->namespaceNames + $validNamespaces;

Most probably the data cache is empty / corrupted and $this->namespaceNames ends up being null which break the sum.

Two possibles fixes would be:

• use array_merge() if it supports merging an array with a null value
• throw a nice exception whenever the getItem calls returns null

Redirecting to General component since that is not really related to unit tests.

Didn't I explain the issue clearly? If the cache is out of date (or not existing) and automatic cache creation is disabled, $dataCache->getItem returns null.

The fix is to enable automatic cache creation for unit tests.

I'm sure I've seen this on the error logs of the cluster

I think it was these tests: https://gerrit.wikimedia.org/r/#/c/6518/

Renaming bug summary