Add oneOf env helper for union values

packages/core/utils/lib/__tests__/env-helper.test.js

@@ -144,4 +144,27 @@ describe('Env helper', () => {
       expect(envHelper.date('DATE_VAR')).toEqual(new Date(2010, 1, 21, 12, 34, 12));
     });
   });
+
+  describe('env with union cast', () => {
+    test('Throws if expectedValues is not provided', () => {
+      expect(() => envHelper.oneOf('NO_VAR')).toThrow();
+    });
+
+    test('Throws if defaultValue not included in expectedValues', () => {
+      expect(() => envHelper.oneOf('NO_VAR', ['lorem', 'ipsum'], 'test')).toThrow();
+    });
+
+    test('Return undefined if value is missing in expectedValues and no defaultValue', () => {
+      expect(envHelper.oneOf('NO_VAR', ['lorem', 'ipsum'])).toBeUndefined();
+    });
+
+    test('Return defaultValue if value does not exist in expectedValues', () => {
+      expect(envHelper.oneOf('NO_VAR', ['lorem', 'ipsum'], 'ipsum')).toBe('ipsum');
+    });
+
+    test('Return defaultValue if value exists and is missing in expectedValues', () => {
+      process.env.WITH_VAR = 'test';
+      expect(envHelper.oneOf('WITH_VAR', ['lorem', 'ipsum'], 'ipsum')).toBe('ipsum');
+    });
+  });
 });

packages/core/utils/lib/env-helper.js

@@ -71,6 +71,26 @@ const utils = {
     const value = process.env[key];
     return new Date(value);
   },
+
+  /**
+   * Gets a value from env that matches oneOf provided values
+   * @param {string} key
+   * @param {string[]} expectedValues
+   * @param {string|undefined} defaultValue
+   * @returns {string|undefined}
+   */
+  oneOf(key, expectedValues, defaultValue) {
+    if (!expectedValues) {
+      throw new Error(`env.oneOf requires expectedValues`);
+    }
+
+    if (defaultValue && !expectedValues.includes(defaultValue)) {
+      throw new Error(`env.oneOf requires defaultValue to be included in expectedValues`);
+    }
+
+    const rawValue = env(key, defaultValue);
+    return expectedValues.includes(rawValue) ? rawValue : defaultValue;
+  },
 };
 
 Object.assign(env, utils);