Better tests when loading multiple packages

src/pyodide.js

@@ -49,8 +49,6 @@ var languagePluginLoader = new Promise((resolve, reject) => {
         package_uri = 'default channel';
       }
 
-      console.log(`Loading ${package} from ${package_uri}`);
-
       if (package in loadedPackages) {
         if (package_uri != loadedPackages[package]) {
           throw new Error(
@@ -58,7 +56,16 @@ var languagePluginLoader = new Promise((resolve, reject) => {
               `${package} from ${package_uri} while it is already ` +
               `loaded from ${loadedPackages[package]}!`);
         }
+      } else if (package in toLoad) {
+        if (package_uri != toLoad[package]) {
+          throw new Error(
+              `URI mismatch, attempting to load package ` +
+              `${package} from ${package_uri} while it is already ` +
+              `being loaded from ${toLoad[package]}!`);
+        }
       } else {
+        console.log(`Loading ${package} from ${package_uri}`);
+
         toLoad[package] = package_uri;
         if (packages.hasOwnProperty(package)) {
           packages[package].forEach((subpackage) => {

test/test_package_loading.py

@@ -37,8 +37,12 @@ def test_invalid_package_name(selenium):
         selenium.load_package('tcp://some_url')
 
 
-def test_load_packages_multiple(selenium):
-    selenium.load_package(['pyparsing', 'pytz'])
+def test_load_packages_multiple(selenium_standalone):
+    selenium = selenium_standalone
+    selenium.load_package(['pyparsing', 'matplotlib'])
+    selenium.run('import pyparsing')
+    selenium.run('import matplotlib')
+    assert selenium.logs.count('Loading pyparsing') == 1
 
 
 @pytest.mark.xfail(reason='Not implemented')