Add getOptionalEnvVar function

Also add tests for it and `getRequiredEnvParam`

src/util.test.ts

@@ -252,6 +252,35 @@ test("allowed API versions", async (t) => {
   );
 });
 
+test("getRequiredEnvParam - gets environment variables", (t) => {
+  process.env.SOME_UNIT_TEST_VAR = "foo";
+  const result = util.getRequiredEnvParam("SOME_UNIT_TEST_VAR");
+  t.is(result, "foo");
+});
+
+test("getRequiredEnvParam - throws if an environment variable isn't set", (t) => {
+  t.throws(() => util.getRequiredEnvParam("SOME_UNIT_TEST_VAR"));
+});
+
+test("getOptionalEnvVar - gets environment variables", (t) => {
+  process.env.SOME_UNIT_TEST_VAR = "foo";
+  const result = util.getOptionalEnvVar("SOME_UNIT_TEST_VAR");
+  t.is(result, "foo");
+});
+
+test("getOptionalEnvVar - gets undefined for empty environment variables", (t) => {
+  process.env.SOME_UNIT_TEST_VAR = "";
+  const result = util.getOptionalEnvVar("SOME_UNIT_TEST_VAR");
+  t.is(result, undefined);
+});
+
+test("getOptionalEnvVar - doesn't throw for undefined environment variables", (t) => {
+  t.notThrows(() => {
+    const result = util.getOptionalEnvVar("SOME_UNIT_TEST_VAR");
+    t.is(result, undefined);
+  });
+});
+
 test("doesDirectoryExist", async (t) => {
   // Returns false if no file/dir of this name exists
   t.false(util.doesDirectoryExist("non-existent-file.txt"));

src/util.ts

@@ -673,6 +673,17 @@ export function getRequiredEnvParam(paramName: string): string {
   return value;
 }
 
+/**
+ * Get an environment variable, but return `undefined` if it is not set or empty.
+ */
+export function getOptionalEnvVar(paramName: string): string | undefined {
+  const value = process.env[paramName];
+  if (value?.trim().length === 0) {
+    return undefined;
+  }
+  return value;
+}
+
 export class HTTPError extends Error {
   public status: number;