diff --git a/packages/arcgis-rest-request/test/utils/encode-form-data.test.ts b/packages/arcgis-rest-request/test/utils/encode-form-data.test.ts
index 841e358c36..622d10c1f2 100644
--- a/packages/arcgis-rest-request/test/utils/encode-form-data.test.ts
+++ b/packages/arcgis-rest-request/test/utils/encode-form-data.test.ts
@@ -3,6 +3,7 @@ import {
   requiresFormData,
   processParams
 } from "../../src/utils/process-params";
+import { attachmentFile } from "../../../arcgis-rest-feature-service/test/attachments.test";
 
 describe("encodeFormData", () => {
   it("should encode in form data for multipart requests", () => {
@@ -63,4 +64,49 @@ describe("encodeFormData", () => {
         "myNumber=380"
     );
   });
+
+  it("should switch to form data if any item is not a basic type", () => {
+    const dateValue = 1471417200000;
+    const file = attachmentFile();
+    if (!file.name) {
+      // The file's name is used for adding files to a form, so supply a name when we're in a testing
+      // environment that doesn't support File (attachmentFile creates a File with the name "foo.txt"
+      // if File is supported and a file stream otherwise)
+      file.name = "foo.txt";
+    }
+
+    // null, undefined, function are excluded. If you want to send an empty key you need to send an empty string "".
+    // See https://github.com/Esri/arcgis-rest-js/issues/18
+    const params = {
+      myArray1: new Array(8),
+      myArray2: [1, 2, 4, 16],
+      myArray3: [{ a: 1, b: 2 }, { c: "abc" }],
+      myDate: new Date(dateValue),
+      myFunction: () => {
+        return 3.1415;
+      },
+      myBoolean: true,
+      myString: "Hello, world!",
+      myEmptyString: "",
+      myNumber: 380,
+      file
+    };
+
+    expect(requiresFormData(params)).toBeTruthy();
+
+    const formData = processParams(params);
+    expect(typeof formData).toBe("object");
+    expect(formData.myArray1).toBe(",,,,,,,");
+    expect(formData.myArray2).toBe("1,2,4,16");
+    expect(formData.myArray3).toBe('[{"a":1,"b":2},{"c":"abc"}]');
+    expect(formData.myDate).toBe(dateValue);
+    expect(formData.myBoolean).toBeTruthy();
+    expect(formData.myString).toBe("Hello, world!");
+    expect(formData.myEmptyString).toBe("");
+    expect(formData.myNumber).toBe(380);
+    expect(typeof formData.file).toBe("object");
+
+    const encodedFormData = encodeFormData(params);
+    expect(encodedFormData instanceof FormData).toBeTruthy();
+  });
 });