diff --git a/services/web/karma.conf.js b/services/web/karma.conf.js
index b9c8bd8533..7136a19b54 100644
--- a/services/web/karma.conf.js
+++ b/services/web/karma.conf.js
@@ -14,6 +14,7 @@ module.exports = function (config) {
     browsers: ['ChromeCustom'],
     files: [
       'test/unit_frontend/js/bootstrap.js',
+      'test/unit_frontend/es/es-bootstrap.js',
       // Angular must be loaded before requirejs to set up angular global
       'public/js/libs/angular-1.6.4.min.js',
       'public/js/libs/angular-mocks.js',
diff --git a/services/web/test/unit_frontend/es/es-bootstrap.js b/services/web/test/unit_frontend/es/es-bootstrap.js
new file mode 100644
index 0000000000..3fc951e3b9
--- /dev/null
+++ b/services/web/test/unit_frontend/es/es-bootstrap.js
@@ -0,0 +1,19 @@
+/* global chai */
+
+/**
+ * Add chai assertion for comparing CodeMirror Pos objects.
+ * A deep comparison will fail because CodeMirror inserts additional properties
+ * that we want to ignore.
+ */
+chai.Assertion.addMethod('equalPos', function (expectedPos) {
+  const { line: actualLine, ch: actualCh } = this._obj
+  const { line: expectedLine, ch: expectedCh } = expectedPos
+
+  this.assert(
+    actualLine === expectedLine && actualCh === expectedCh,
+    `expected #{exp} to equal #{act}`,
+    `expected #{exp} to not equal #{act}`,
+    `Pos({ line: ${expectedLine}, ch: ${expectedCh} })`,
+    `Pos({ line: ${actualLine}, ch: ${actualCh} })`
+  )
+})