replaced hardcoded API URL with environment variable

.env.example

@@ -0,0 +1 @@
+REACT_APP_POLICYENGINE_API=https://api.policyengine.org

Makefile

@@ -2,6 +2,7 @@ REACT_APP_DEBUG ?= false
 
 install:
 	npm ci
+	cp .env.example .env
 	pip3 install -U black
 
 build:

src/__tests__/api/call.test.js

@@ -1,6 +1,7 @@
 import { renderHook } from "@testing-library/react";
 import { useAuthenticatedApiCall } from "../../api/call";
 import * as authenticatedFetch from "../../hooks/useAuthenticatedFetch";
+import { POLICYENGINE_API } from "../../constants";
 
 jest.mock("../../hooks/useAuthenticatedFetch");
 let mock_authenticated_fetch;
@@ -36,7 +37,7 @@ describe("useAuthenticatedApiCall", () => {
 
     expect(response).toEqual(DEFAULT_FETCH_RESULT);
     expect(mock_authenticated_fetch.mock.calls[0]).toEqual([
-      "https://api.policyengine.org/test/path",
+      POLICYENGINE_API + "/test/path",
       {
         body: JSON.stringify(SOME_REQUEST_BODY),
         headers: {

src/api/call.js

@@ -3,8 +3,7 @@ import { buildParameterTree } from "./parameters";
 import { buildVariableTree, getTreeLeavesInOrder } from "./variables";
 import { wrappedJsonStringify, wrappedResponseJson } from "../data/wrappedJson";
 import { useAuthenticatedFetch } from "../hooks/useAuthenticatedFetch";
-
-const POLICYENGINE_API = "https://api.policyengine.org";
+import { POLICYENGINE_API } from "../constants";
 
 /**
  * returns an api call function that can be used to make requests

src/constants.js

@@ -0,0 +1,2 @@
+export const POLICYENGINE_API =
+  process.env.REACT_APP_POLICYENGINE_API || "https://api.policyengine.org";