# All files / helpers generate-fid.test.ts

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     /**
     * @license
     * Copyright 2019 Google Inc.
     *
     * Licensed under the Apache License, Version 2.0 (the "License");
     * you may not use this file except in compliance with the License.
     * You may obtain a copy of the License at
     *
     *   http://www.apache.org/licenses/LICENSE-2.0
     *
     * Unless required by applicable law or agreed to in writing, software
     * distributed under the License is distributed on an "AS IS" BASIS,
     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     * See the License for the specific language governing permissions and
     * limitations under the License.
     */

    import { expect } from 'chai';
    import { stub } from 'sinon';
    import '../testing/setup';
    import { generateFid } from './generate-fid';

    /** A few random values to generate a FID from. */
    // prettier-ignore
    const MOCK_RANDOM_VALUES = [
      [14, 107, 44, 183, 190, 84, 253, 45, 219, 233, 43, 190, 240, 152, 195, 222, 237],
      [184, 251, 91, 157, 125, 225, 209, 15, 116, 66, 46, 113, 194, 126, 16, 13, 226],
      [197, 123, 13, 142, 239, 129, 252, 139, 156, 36, 219, 192, 153, 52, 182, 231, 177],
      [69, 154, 197, 91, 156, 196, 125, 111, 3, 67, 212, 132, 169, 11, 14, 254, 125],
      [193, 102, 58, 19, 244, 69, 36, 135, 170, 106, 98, 216, 246, 209, 24, 155, 149],
      [252, 59, 222, 160, 82, 160, 82, 186, 14, 172, 196, 114, 146, 191, 196, 194, 146],
      [64, 147, 153, 236, 225, 142, 235, 109, 184, 249, 174, 127, 33, 238, 227, 172, 111],
      [129, 137, 136, 120, 248, 206, 253, 78, 159, 201, 216, 15, 246, 80, 118, 185, 211],
      [117, 150, 2, 180, 116, 230, 45, 188, 183, 43, 152, 100, 50, 255, 101, 175, 190],
      [156, 129, 30, 101, 58, 137, 217, 249, 12, 227, 235, 80, 248, 81, 191, 2, 5],
      [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
      [255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255],
    ]

    /** The FIDs that should be generated based on MOCK_RANDOM_VALUES. */
    const EXPECTED_FIDS = [
      'fmsst75U_S3b6Su-8JjD3u',
      'ePtbnX3h0Q90Qi5xwn4QDe',
      'dXsNju-B_IucJNvAmTS257',
      'dZrFW5zEfW8DQ9SEqQsO_n',
      'cWY6E_RFJIeqamLY9tEYm5',
      'fDveoFKgUroOrMRykr_Ewp',
      'cJOZ7OGO6224-a5_Ie7jrG',
      'cYmIePjO_U6fydgP9lB2ud',
      'dZYCtHTmLby3K5hkMv9lr7',
      'fIEeZTqJ2fkM4-tQ-FG_Ag',
      'cAAAAAAAAAAAAAAAAAAAAA',
      'f_____________________'
    ];

    const VALID_FID = /^[cdef][A-Za-z0-9_-]{21}$/;

    describe('generateFid', () => {
      it('deterministically generates FIDs based on crypto.getRandomValues', () => {
        let randomValueIndex = 0;
        stub(crypto, 'getRandomValues').callsFake(array => {
          if (!(array instanceof Uint8Array)) {
            throw new Error('what');
          }
          const values = MOCK_RANDOM_VALUES[randomValueIndex++];
          for (let i = 0; i < array.length; i++) {
            array[i] = values[i];
          }
          return array;
        });

        for (const expectedFid of EXPECTED_FIDS) {
          expect(generateFid()).to.deep.equal(expectedFid);
        }
      });

      it('generates valid FIDs', () => {
        for (let i = 0; i < 1000; i++) {
          const fid = generateFid();
          expect(VALID_FID.test(fid)).to.equal(true, `${fid} is not a valid FID`);
        }
      });

      it('generates FIDs where each character is equally likely to appear in each location', () => {
        const numTries = 200000;

        const charOccurrencesMapList: Array<Map<string, number>> = new Array(22);
        for (let i = 0; i < charOccurrencesMapList.length; i++) {
          charOccurrencesMapList[i] = new Map();
        }

        for (let i = 0; i < numTries; i++) {
          const fid = generateFid();

          Array.from(fid).forEach((char, location) => {
            const map = charOccurrencesMapList[location];
            map.set(char, (map.get(char) || 0) + 1);
          });
        }

        for (let i = 0; i < charOccurrencesMapList.length; i++) {
          const map = charOccurrencesMapList[i];
          if (i === 0) {
            // In the first location only 4 characters (c, d, e, f) are valid.
            expect(map.size).to.equal(4);
          } else {
            // In locations other than the first, all 64 characters are valid.
            expect(map.size).to.equal(64);
          }

          Array.from(map.entries()).forEach(([_, occurrence]) => {
            const expectedOccurrence = numTries / map.size;

            // 10% margin of error
            expect(occurrence).to.be.above(expectedOccurrence * 0.9);
            expect(occurrence).to.be.below(expectedOccurrence * 1.1);
          });
        }
      }).timeout(30000);
    });