fix: contains operator does not support Drop, fixes #492

test/e2e/issues.ts

@@ -1,4 +1,4 @@
-import { Liquid } from '../..'
+import { Liquid, Drop } from '../..'
 import { expect, use } from 'chai'
 import * as chaiAsPromised from 'chai-as-promised'
 import * as sinon from 'sinon'
@@ -232,4 +232,13 @@ describe('Issues', function () {
     const html = await engine.parseAndRender(`{% assign a = "x,y,z" | split: ',' -%}{{ a[-1] }} {{ a[-3] }} {{ a[-8] }}`)
     expect(html).to.equal('z x ')
   })
+  it('#492 contains operator does not support Drop', async () => {
+    class TemplateDrop extends Drop {
+      valueOf () { return 'product' }
+    }
+    const engine = new Liquid()
+    const ctx = { template: new TemplateDrop() }
+    const html = await engine.parseAndRender(`{% if template contains "product" %}contains{%endif%}`, ctx)
+    expect(html).to.equal('contains')
+  })
 })