Add test to check if symbols in confirmation code are distributed uni…

…formly

web-dapp/test/server/generate_code.spec.js

@@ -4,6 +4,22 @@ const generate_code = require('../../server-lib/generate_code');
 const config = require('../../server-config');
 
 const TRIES = 1e4;
+const EXPECTED_FREQ = 1.0/config.code_symbols.length;
+const MAX_DIFF = EXPECTED_FREQ*5e-2;
+
+function safe_inc(obj, key, val = 1) {
+    if (!obj[key]) {
+        obj[key] = 0;
+    }
+    obj[key] += val;
+}
+
+function a_in_b(a,b) {
+    for (var j = 0; j < a.length; j++) {
+        if (b.indexOf(a[j]) < 0) return false;
+    }
+    return true;
+}
 
 describe('Confirmation code', () => {
     it('cc length should be equal to the one in config', () => {
@@ -19,4 +35,39 @@ describe('Confirmation code', () => {
 
         return expect(pass).toEqual(true);
     });
+
+    it('cc symbols should be roughly equiprobable', () => {
+        let symbs_stat = {};
+        for (let i = 0; i < TRIES; i++) {
+            let code = generate_code();
+            for (let j = 0; j < code.length; j++) {
+                safe_inc(symbs_stat, code[j]);
+            }
+        }
+
+        // 1. check that all symbols are present
+        let symbs = Object.keys(symbs_stat);
+        expect(symbs.length === config.code_symbols.length);
+        expect(a_in_b(symbs, config.code_symbols)).toEqual(true);
+        expect(a_in_b(config.code_symbols, symbs)).toEqual(true);
+
+        // 2. check frequencies
+        let freqs_stat = {};
+        for (let i = 0; i < symbs.length; i++) {
+            freqs_stat[symbs[i]] = symbs_stat[symbs[i]]/(TRIES*config.code_length);
+        }
+
+        let freqs = Object.keys(freqs_stat);
+
+        let max_diff = 0;
+        let EXPECTED_FREQ = 1.0/config.code_symbols.length;
+        for (let i = 0; i < freqs.length; i++) {
+            let diff = Math.abs( freqs_stat[freqs[i]] - EXPECTED_FREQ );
+            if (diff > max_diff) {
+                max_diff = diff;
+            }
+        }
+
+        expect(max_diff < MAX_DIFF).toEqual(true);
+    });
 });