From 6c892c4b2f9942e73361fb8d43fe10158fc581f1 Mon Sep 17 00:00:00 2001
From: Oleksii Trekhleb <trehleb@gmail.com>
Date: Tue, 5 Jun 2018 21:50:08 +0300
Subject: [PATCH] Fix bug with primality test.

---
 src/algorithms/math/primality-test/README.md      | 15 +++++++++++++--
 .../primality-test/__test__/trialDivision.test.js |  5 +++++
 .../math/primality-test/trialDivision.js          |  5 +++++
 3 files changed, 23 insertions(+), 2 deletions(-)

diff --git a/src/algorithms/math/primality-test/README.md b/src/algorithms/math/primality-test/README.md
index fd5af656..8a9852dc 100644
--- a/src/algorithms/math/primality-test/README.md
+++ b/src/algorithms/math/primality-test/README.md
@@ -1,6 +1,16 @@
 # Primality Test
 
-A primality test is an algorithm for determining whether an input 
+A **prime number** (or a **prime**) is a natural number greater than `1` that 
+cannot be formed by multiplying two smaller natural numbers. A natural number 
+greater than `1` that is not prime is called a composite number. For 
+example, `5` is prime because the only ways of writing it as a 
+product, `1 × 5` or `5 × 1`, involve `5` itself. However, `6` is 
+composite because it is the product of two numbers `(2 × 3)` that are 
+both smaller than `6`. 
+
+![Prime Numbers](https://upload.wikimedia.org/wikipedia/commons/f/f0/Primes-vs-composites.svg)
+
+A **primality test** is an algorithm for determining whether an input 
 number is prime. Among other fields of mathematics, it is used 
 for cryptography. Unlike integer factorization, primality tests 
 do not generally give prime factors, only stating whether the 
@@ -11,4 +21,5 @@ size of the input).
 
 ## References
 
-[Wikipedia](https://en.wikipedia.org/wiki/Primality_test)
+- [Prime Numbers on Wikipedia](https://en.wikipedia.org/wiki/Prime_number)
+- [Primality Test on Wikipedia](https://en.wikipedia.org/wiki/Primality_test)
diff --git a/src/algorithms/math/primality-test/__test__/trialDivision.test.js b/src/algorithms/math/primality-test/__test__/trialDivision.test.js
index d4f54d47..26080857 100644
--- a/src/algorithms/math/primality-test/__test__/trialDivision.test.js
+++ b/src/algorithms/math/primality-test/__test__/trialDivision.test.js
@@ -23,6 +23,11 @@ function primalityTest(testFunction) {
   expect(testFunction(192)).toBeFalsy();
   expect(testFunction(200)).toBeFalsy();
   expect(testFunction(400)).toBeFalsy();
+
+  // It should also deal with floats.
+  expect(testFunction(0.5)).toBeFalsy();
+  expect(testFunction(1.3)).toBeFalsy();
+  expect(testFunction(10.5)).toBeFalsy();
 }
 
 describe('trialDivision', () => {
diff --git a/src/algorithms/math/primality-test/trialDivision.js b/src/algorithms/math/primality-test/trialDivision.js
index 64e62472..f4d7c2b6 100644
--- a/src/algorithms/math/primality-test/trialDivision.js
+++ b/src/algorithms/math/primality-test/trialDivision.js
@@ -3,6 +3,11 @@
  * @return {boolean}
  */
 export default function trialDivision(number) {
+  // Check if number is integer.
+  if (number % 1 !== 0) {
+    return false;
+  }
+
   if (number <= 1) {
     // If number is less than one then it isn't prime by definition.
     return false;