reset environment variables between tests

lib/testing-utils.js

@@ -51,6 +51,11 @@ function setupTests(test) {
         const processStderrWrite = process.stderr.write.bind(process.stderr);
         t.context.stderrWrite = processStderrWrite;
         process.stderr.write = wrapOutput(t.context);
+        // Many tests modify environment variables. Take a copy now so that
+        // We reset them after the test to keep tests independent of each other.
+        // process.env only has strings fields, so a shallow copy is fine.
+        t.context.env = {};
+        Object.assign(process.env, t.context.env);
     });
     typedTest.afterEach.always(t => {
         // Restore stdout and stderr
@@ -62,6 +67,8 @@ function setupTests(test) {
         }
         // Undo any modifications made by sinon
         sinon_1.default.restore();
+        // Undo any modifications to the env
+        process.env = t.context.env;
     });
 }
 exports.setupTests = setupTests;