Add tests for cache

Author: hannahramadan

helpers/sql-obfuscation/test/helpers/query_summary/cache_test.rb

@@ -17,4 +17,39 @@ def test_fetch_returns_value_when_key_exists
 
     assert_equal 'value1', result
   end
+
+  def test_eviction_when_cache_size_exceeded
+    small_cache = OpenTelemetry::Helpers::QuerySummary::Cache.new(size: 2)
+
+    small_cache.fetch('key1') { 'value1' }
+    small_cache.fetch('key2') { 'value2' }
+    small_cache.fetch('key3') { 'value3' }
+
+    result = small_cache.fetch('key1') { 'new_value1' }
+    assert_equal 'new_value1', result
+  end
+
+  def test_cache_thread_safety
+    threads = Array.new(10) do |i|
+      Thread.new do
+        @cache.fetch('shared_key') { "thread_#{i}_value" }
+      end
+    end
+
+    results = threads.map(&:value)
+
+    assert_equal 1, results.uniq.size
+  end
+
+  def test_empty_string
+    @cache.fetch('') { 'empty_string_value' }
+
+    assert_equal 'empty_string_value', @cache.fetch('')
+  end
+
+  def test_nil
+    @cache.fetch(nil) { 'nil_value' }
+
+    assert_equal 'nil_value', @cache.fetch(nil)
+  end
 end