Replace assertions involving calls to isset() with assertArrayHasKey()/assertArrayNotHasKey

Problem/Motivation

As title

Proposed resolution

Remove redundant assertion messages at the same time.

Example:

-    $this->assertTrue(isset($ids['entity_test.entity_test.field_test_import']));
+    $this->assertArrayHasKey('entity_test.entity_test.field_test_import', $ids);