diff --git a/js/test.js b/js/test.js
index f328b51..6f193f1 100644
--- a/js/test.js
+++ b/js/test.js
@@ -277,7 +277,7 @@ describe('Helper', function () {
                     var key = item.replace(/[\s;,=]/g, Array(i+2).join('£')),
                         value = (values[i] || values[0]).replace(/[\s;,=]/g, '');
                     cookieArray.push(key + '=' + value);
-                    if (Math.random() < 1 / i)
+                    if (Math.random() < 1 / i || selectedKey === key)
                     {
                         selectedKey = key;
                         selectedValue = value;
diff --git a/tst/README.md b/tst/README.md
index 76e69ee..e11bc49 100644
--- a/tst/README.md
+++ b/tst/README.md
@@ -2,7 +2,7 @@ Running PHP unit tests
 ======================
 
 In order to run these tests, you will need to install the following packages
-and its dependencies:
+and their dependencies:
 * phpunit
 * php-gd
 * php-sqlite3
@@ -13,12 +13,30 @@ Example for Debian and Ubuntu:
 $ sudo apt install phpunit php-gd php-sqlite php-xdebug
 ```
 
-To run the tests, just change into this directory and run phpunit:
+To run the tests, change into the `tst` directory and run phpunit:
 ```console
 $ cd PrivateBin/tst
 $ phpunit
 ```
 
+Additionally there is the `ConfigurationTestGenerator`. Based on the
+configurations defined in its constructor, it generates the unit test file
+`tst/ConfigurationCombinationsTest.php`, containing all possible combinations
+of these configurations and tests for (most of the) valid combinations. Some of
+combinations can't be tested with this method, i.e. a valid option combined with
+an invalid one. Other very specific test cases (i.e. to trigger multiple errors)
+are covered in `tst/PrivateBinTest.php`. Here is how to generate the
+configuration test and run it:
+
+```console
+$ cd PrivateBin/tst
+$ php ConfigurationTestGenerator.php
+$ phpunit ConfigurationCombinationsTest.php
+```
+
+Note that it can take an hour or longer to run the several thousand tests.
+
+
 Running JavaScript unit tests
 =============================
 
@@ -36,8 +54,8 @@ $ cd PrivateBin/js
 $ npm install jsverify jsdom jsdom-global
 ```
 
-Example for Debian and Ubuntu, including steps to allow current user to install
-node modules globally:
+Example for Debian and Ubuntu, including steps to allow the current user to
+install node modules globally:
 ```console
 $ sudo apt install npm
 $ sudo mkdir /usr/local/lib/node_modules
@@ -54,3 +72,46 @@ $ cd PrivateBin/js
 $ istanbul cover _mocha
 ```
 
+Property based unit testing
+---------------------------
+
+In the JavaScript unit tests we use the JSVerify library to leverage property
+based unit testing. Instead of artificially creating specific test cases to
+cover all relevant paths of the tested code (with the generated coverage reports
+providing means to check the tested paths), property based testing allows us to
+describe the patterns of data that are valid input.
+
+With each run of the tests, for each `jsc.property` 100 random inputs are
+generated and tested. For example we tell the test to generate random strings,
+which will include empty strings, numeric strings, long strings, unicode
+sequences, etc. This is great for finding corner cases that one might not think
+of when explicitly writing one test case at a time.
+
+There is another benefit, too: When an error is found, JSVerify will try to find
+the smallest, still failing test case for you and print this out including the
+associated random number generator (RNG) state, so you can reproduce it easily:
+
+```console
+[...]
+
+  30 passing (3s)
+  1 failing
+
+  1) Helper getCookie returns the requested cookie:
+     Error: Failed after 30 tests and 11 shrinks. rngState: 88caf85079d32e416b; Counterexample: ["{", "9", "9", "YD8%fT"]; [" ", "_|K:"]; 
+
+[...]
+```
+
+Of course it may just be that you need to adjust a test case if the random
+pattern generated is ambiguous. In the above example the cookie string would
+contain two identical keys "9", something that may not be valid, but that our
+code could encounter and needs to be able to handle.
+
+After you adjusted the code of the library or the test you can rerun the test
+with the same RNG state as follows:
+
+```console
+$ istanbul cover _mocha -- test.js --jsverifyRngState 88caf85079d32e416b
+```
+