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poisson_distribution.test.js
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poisson_distribution.test.js
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/* eslint no-shadow: 0 */
const test = require("tap").test;
const ss = require("../dist/simple-statistics.js");
function rnd(n) {
return parseFloat(n.toFixed(4));
}
// expected cumulative probabilities taken from Appendix 1, Table I of William W. Hines & Douglas C.
// Montgomery, "Probability and Statistics in Engineering and Management Science", Wiley (1980).
test("poissonDistribution", function (t) {
t.test(
"can return generate probability and cumulative probability distributions for lambda = 3.0",
function (t) {
t.equal("object", typeof ss.poissonDistribution(3.0));
t.equal(rnd(ss.poissonDistribution(3.0)[3]), 0.224, ss.epsilon);
t.end();
}
);
t.test(
"can generate probability and cumulative probability distributions for lambda = 4.0",
function (t) {
t.equal("object", typeof ss.poissonDistribution(4.0));
t.equal(rnd(ss.poissonDistribution(4.0)[2]), 0.1465, ss.epsilon);
t.end();
}
);
t.test(
"can generate probability and cumulative probability distributions for lambda = 5.5",
function (t) {
t.equal("object", typeof ss.poissonDistribution(5.5));
t.equal(rnd(ss.poissonDistribution(5.5)[7]), 0.1234, ss.epsilon);
t.end();
}
);
t.test(
"can generate probability and cumulative probability distributions for lambda = 9.5",
function (t) {
t.equal("object", typeof ss.poissonDistribution(9.5));
t.equal(rnd(ss.poissonDistribution(9.5)[17]), 0.0088, ss.epsilon);
t.end();
}
);
t.test("can return undefined when lambda <= 0", function (t) {
t.equal(undefined, ss.poissonDistribution(0));
t.equal(undefined, ss.poissonDistribution(-10));
t.end();
});
t.end();
});