diff --git a/spec/lib/search_index_backend_spec.rb b/spec/lib/search_index_backend_spec.rb
new file mode 100644
index 000000000..708f9a955
--- /dev/null
+++ b/spec/lib/search_index_backend_spec.rb
@@ -0,0 +1,101 @@
+require 'rails_helper'
+
+RSpec.describe SearchIndexBackend do
+  describe '.build_query' do
+    subject(:query) { SearchIndexBackend.build_query('', query_extension: params) }
+    let(:params) { { 'bool' => { 'filter' => { 'term' => { 'a' => 'b' } } } } }
+
+    it 'coerces :query_extension hash keys to symbols' do
+      expect(query.dig(:query, :bool, :filter, :term, :a)).to eq('b')
+    end
+  end
+
+  describe '.search' do
+    subject(:search) { SearchIndexBackend.search(query, index, limit: 3000) }
+
+    context 'for query with no results' do
+      let(:query) { 'preferences.notification_sound.enabled:*' }
+
+      context 'on a single index' do
+        let(:index) { 'User' }
+
+        it { is_expected.to be_nil }
+      end
+
+      context 'on multiple indices' do
+        let(:index) { %w[User Organization] }
+
+        it { is_expected.to be_an(Array).and not_include(nil).and be_empty }
+      end
+    end
+  end
+
+  describe '.append_wildcard_to_simple_query' do
+    context 'with "simple" queries' do
+      let(:queries) { <<~QUERIES.lines.map { |x| x.split('#')[0] }.map(&:strip) }
+        M
+        Max
+        Max. # dot and underscore are acceptable characters in simple queries
+        A_
+        A_B
+        äöü
+        123
+        *ax  # wildcards are allowed in simple queries
+        Max*
+        M*x
+        M?x
+        test@example.com
+        test@example.
+        test@example
+        test@
+      QUERIES
+
+      it 'appends a * to the original query' do
+        expect(queries.map(&SearchIndexBackend.method(:append_wildcard_to_simple_query)))
+          .to eq(queries.map { |q| "#{q}*" })
+      end
+    end
+
+    context 'with "complex" queries (using search operators)' do
+      let(:queries) { <<~QUERIES.lines.map { |x| x.split('#')[0] }.map(&:strip) }
+        title:"some words with spaces" # exact phrase / without quotation marks " an AND search for the words will be performed (in Zammad 1.5 and lower an OR search will be performed)
+        title:"some wor*" # exact phrase beginning with "some wor*" will be searched
+        created_at:[2017-01-01 TO 2017-12-31] # a time range
+        created_at:>now-1h # created within last hour
+        state:new OR state:open
+        (state:new OR state:open) OR priority:"3 normal"
+        (state:new OR state:open) AND customer.lastname:smith
+        state:(new OR open) AND title:(full text search) # state: new OR open & title: full OR text OR search
+        tags: "some tag"
+        owner.email: "bod@example.com" AND state: (new OR open OR pending*) # show all open tickets of a certain agent
+        state:closed AND _missing_:tag # all closed objects without tags
+        article_count: [1 TO 5] # tickets with 1 to 5 articles
+        article_count: [10 TO *] # tickets with 10 or more articles
+        article.from: bob # also article.from can be used
+        article.body: heat~ # using the fuzzy operator will also find terms that are similar, in this case also "head"
+        article.body: /joh?n(ath[oa]n)/ # using regular expressions
+        user:M
+        user:Max
+        user:Max.
+        user:Max*
+        organization:A_B
+        organization:A_B*
+        user: M
+        user: Max
+        user: Max.
+        user: Max*
+        organization: A_B
+        organization: A_B*
+        id:123
+        number:123
+        id:"123"
+        number:"123"
+      QUERIES
+
+      it 'returns the original query verbatim' do
+        expect(queries.map(&SearchIndexBackend.method(:append_wildcard_to_simple_query)))
+          .to eq(queries)
+      end
+    end
+  end
+end
diff --git a/spec/support/negated_matchers.rb b/spec/support/negated_matchers.rb
index 93f5b66e5..539f78048 100644
--- a/spec/support/negated_matchers.rb
+++ b/spec/support/negated_matchers.rb
@@ -1 +1,2 @@
 RSpec::Matchers.define_negated_matcher :not_change, :change
+RSpec::Matchers.define_negated_matcher :not_include, :include
diff --git a/test/unit/search_index_backend_test.rb b/test/unit/search_index_backend_test.rb
deleted file mode 100644
index dbe2a230f..000000000
--- a/test/unit/search_index_backend_test.rb
+++ /dev/null
@@ -1,95 +0,0 @@
-require 'test_helper'
-
-class SearchIndexBackendTest < ActiveSupport::TestCase
-  test 'query extension keys are normalized to symbols' do
-    query_strings = SearchIndexBackend.build_query('', query_extension: { 'bool' => { 'filter' => { 'term' => { 'a' => 'b' } } } })
-    query_symbols = SearchIndexBackend.build_query('', query_extension: { bool: { filter: { term: { a: 'b' } } } })
-
-    assert_equal query_strings, query_symbols
-    assert_not_nil query_strings.dig(:query, :bool, :filter, :term, :a)
-  end
-
-  test 'search with ES off never returns nil in array' do
-    index_one   = SearchIndexBackend.search('preferences.notification_sound.enabled:*', 'User', limit: 3000)
-    index_multi = SearchIndexBackend.search('preferences.notification_sound.enabled:*', %w[User Organization], limit: 3000)
-
-    assert_nil index_one
-    assert index_multi.empty?
-  end
-
-  test 'simple_query_append_wildcard correctly modifies simple queries' do
-    def clean_queries(query_string)
-      query_string.each_line
-                  .map(&:strip)
-                  .reject(&:empty?)
-                  .map { |x| x.split('#')[0] }
-    end
-
-    # Examples of complex queries from https://docs.zammad.org/en/latest/general-search.html
-    complex_queries = clean_queries %(
-        title:”some words with spaces” # exact phrase / without quotation marks ” an AND search for the words will be performed (in Zammad 1.5 and lower an OR search will be performed)
-        title:”some wor*” # exact phrase beginning with “some wor*” will be searched
-        created_at:[2017-01-01 TO 2017-12-31] # a time range
-        created_at:>now-1h # created within last hour
-        state:new OR state:open
-        (state:new OR state:open) OR priority:”3 normal”
-        (state:new OR state:open) AND customer.lastname:smith
-        state:(new OR open) AND title:(full text search) # state: new OR open & title: full OR text OR search
-        tags: “some tag”
-        owner.email: “bod@example.com” AND state: (new OR open OR pending*) # show all open tickets of a certain agent
-        state:closed AND _missing_:tag # all closed objects without tags
-        article_count: [1 TO 5] # tickets with 1 to 5 articles
-        article_count: [10 TO *] # tickets with 10 or more articles
-        article.from: bob # also article.from can be used
-        article.body: heat~ # using the fuzzy operator will also find terms that are similar, in this case also “head”
-        article.body: /joh?n(ath[oa]n)/ # using regular expressions
-        user:M
-        user:Max
-        user:Max.
-        user:Max*
-        organization:A_B
-        organization:A_B*
-        user: M
-        user: Max
-        user: Max.
-        user: Max*
-        organization: A_B
-        organization: A_B*
-        id:123
-        number:123
-        id:"123"
-        number:"123"
-    )
-
-    simple_queries = clean_queries %(
-        M
-
-        Max
-        Max. # dot and underscore are acceptable characters in simple queries
-        A_
-        A_B
-        äöü
-        123
-        *ax  # wildcards are allowed in simple queries
-        Max*
-        M*x
-        M?x
-        test@example.com
-        test@example.
-        test@example
-        test@
-    )
-
-    complex_queries.each do |query|
-      result_query = SearchIndexBackend.append_wildcard_to_simple_query(query)
-      # Verify that the result query is still the same as the input query
-      assert_equal(query, result_query)
-    end
-
-    simple_queries.each do |query|
-      result_query = SearchIndexBackend.append_wildcard_to_simple_query(query)
-      # Verify that * is correctly appended to simple queries
-      assert_equal(query + '*', result_query)
-    end
-  end
-end