Alter term creation out to a migration.

... also, identify the term by URI instead of by name, as it's the URI
that is used to related to it from config.

islandora_fits.install

@@ -6,25 +6,22 @@
  */
 
 
-
-use Drupal\taxonomy\Entity\Term;
 use Drupal\field\Entity\FieldConfig;
 
 /**
  * Implements hook_install().
  */
-function islandora_fits_install() {
-  $term_name = 'FITS File';
-  $test_terms = taxonomy_term_load_multiple_by_name($term_name);
-  if (!$test_terms) {
-    $term = Term::create([
-      'parent' => [],
-      'name' => $term_name,
-      'vid' => 'islandora_media_use',
-      'description' => 'Technical Metadata associated with an original media file',
-      'field_external_uri' => ['uri' => 'https://projects.iq.harvard.edu/fits'],
-    ])->save();
+function islandora_fits_install($is_syncing) {
+
+  if (!_islandora_fits_term_exists()) {
+    $callable = $is_syncing ? [\Drupal::messenger(), 'addStatus'] : [\Drupal::messenger(), 'addWarning'];
+    $callable(t('A term in the taxonomy @vid with the URI @uri does not appear to exist. The @migration_id migration can be executed to create it.', [
+      '@vid' => 'islandora_media_use',
+      '@uri' => 'https://projects.iq.harvard.edu/fits',
+      '@migration_id' => 'islandora_fits_tags',
+    ]));
   }
+
   // Add xml extension if it doesn't already exist.
   $field = FieldConfig::load("media.file.field_media_file");
   if ($field) {
@@ -37,3 +34,40 @@ function islandora_fits_install() {
     }
   }
 }
+
+/**
+ * Implements hook_requirements().
+ */
+function islandora_fits_requirements($phase) : array {
+  $requirements = [];
+
+  if ($phase == 'runtime') {
+    $term_exists = _islandora_fits_term_exists();
+    $requirements['islandora_fits_term_exists'] = [
+      'title' => t('FITS Term Exists'),
+      'value' => $term_exists,
+      'description' => t('Whether or not a term with the URI targeted by default FITS derivative configuration exists. If derivative configurations were made to target another URI, this can probably be ignored.'),
+      'severity' => $term_exists ? REQUIREMENT_OK : REQUIREMENT_WARNING
+    ];
+  }
+
+  return $requirements;
+}
+
+/**
+ * Helper; determine if a term with the target URI exists.
+ *
+ * @return bool
+ *   TRUE if a term (at least one) with the target URI exists; otherwise, FALSE.
+ *
+ * @throws \Drupal\Component\Plugin\Exception\InvalidPluginDefinitionException
+ * @throws \Drupal\Component\Plugin\Exception\PluginNotFoundException
+ */
+function _islandora_fits_term_exists() {
+  $query = \Drupal::entityTypeManager()->getStorage('taxonomy_term')->getQuery()
+    ->condition('vid', 'islandora_media_use')
+    ->condition('field_external_uri.uri', 'https://projects.iq.harvard.edu/fits')
+    ->count();
+  $count = $query->execute();
+  return $count > 0;
+}

migrations/islandora_fits_tags.yml

@@ -0,0 +1,25 @@
+---
+id: islandora_fits_tags
+migration_tags:
+  - islandora
+migration_group: islandora
+label: "FITS Term(s)"
+source:
+  plugin: embeddedd_data
+  data_rows:
+    - vid: islandora_media_use
+      name: FITS File
+      description: Technical Metadata associated with an original media file
+      uri: https://projects.iq.harvard.edu/fits
+  ids:
+    uri:
+      type: string
+process:
+  vid: vid
+  name: name
+  description: description
+  field_external_uri/uri: uri
+destination:
+  plugin: entity:taxonomy_term
+migration_dependencies:
+  required: { }