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Delete false positive tests for bloom filter.

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Oleksii Trekhleb 2018-06-30 20:46:34 +03:00
parent 610b120e27
commit a2310c59d3
1 changed files with 0 additions and 86 deletions
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src/data-structures/bloom-filter/__test__/BloomFilterFalsePositive.test.js
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import BloomFilter from '../BloomFilter';
// Adapted from http://stackoverflow.com/questions/1349404/generate-random-string-characters-in-javascript
function makeID() {
const possible = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz';
let id = '';
for (let i = 0; i < 10; i += 1) {
const randomLength = Math.random() * possible.length;
const randomIndex = Math.floor(randomLength);
id += possible.charAt(randomIndex);
}
return id;
}
function run10kTrials(numRandomTests = 1000) {
const bloomFilter = new BloomFilter();
const mockPeopleIDs = [];
for (let i = 0; i < 10; i += 1) {
mockPeopleIDs.push(makeID());
}
mockPeopleIDs.forEach(id => bloomFilter.insert(id));
let numFalsePositives = 0;
for (let index = 0; index < numRandomTests; index += 1) {
const randomID = makeID();
if (bloomFilter.mayContain(randomID)) {
numFalsePositives += 1;
}
}
return numFalsePositives;
}
function testFilter(numTrials = 100) {
const results = [];
for (let i = 0; i < numTrials; i += 1) {
results.push(run10kTrials());
}
const sum = results.reduce((cumulative, next) => cumulative + next, 0);
return sum / numTrials;
}
describe('Bloom filter false positives', () => {
const falsePositiveProbability = 0.0174;
const expectedFalsePositives = falsePositiveProbability * 1000;
const avgFalsePositives = testFilter();
it(`Should keep false positives close to an expected value:
# trials = 1000
k = 3 (hash functions)
m = 100 (size)
n = 10 (items inserted)
Using k, m, and n, plugged into https://hur.st/bloomfilter/?n=3&p=&m=18&k=3
Chance of false positive = 0.017
Expected false positives = # trials * chance of false positive
Expected false positives => 1000 * ${falsePositiveProbability}
Expected false positives => ${expectedFalsePositives}
**************************
EXPECTED = ${expectedFalsePositives}
ACTUAL AVG = ${avgFalsePositives}
**************************
If the expected and actual numbers are far off, something is wrong.
Inspect manually.`, () => {
// We give it a large range to avoid unnecessary failures.
// If it's working correctly, the value should definitely
// fall within this range.
// In over 1,000 test runs, none of them ever come close
// to falling outside of this range.
const upperLimit = expectedFalsePositives + 5;
const lowerLimit = expectedFalsePositives - 5;
expect(avgFalsePositives).toBeGreaterThan(lowerLimit);
expect(avgFalsePositives).toBeLessThan(upperLimit);
});
});