It's possible that search integration test coverage is missing for Solr for the following Field Types:

• Media
• Url
• Image

It relied on .class parameters overrides:

    ezpublish.fieldType.ezfloat.class: eZ\Publish\API\Repository\Tests\FieldType\SearchableFloat
    ezpublish.fieldType.ezimage.class: eZ\Publish\API\Repository\Tests\FieldType\SearchableImage
    ezpublish.fieldType.ezmedia.class: eZ\Publish\API\Repository\Tests\FieldType\SearchableMedia
    ezpublish.fieldType.ezurl.class: eZ\Publish\API\Repository\Tests\FieldType\SearchableUrl 

which were dropped via ezsystems/ezpublish-kernel#2911 for 3.0. Looks like Float is already searchable anyway, however the other mentioned field types are not.

Most likely test matrix silently skips testing those Field Types on Solr. See:

• \eZ\Publish\API\Repository\Tests\FieldType\SearchBaseIntegrationTest::testCreateTestContent
• \eZ\Publish\API\Repository\Tests\FieldType\SearchMultivaluedBaseIntegrationTest::testCreateMultivaluedTestContent