diff --git a/tests/arithmetics/counters.js b/tests/arithmetics/counters.js
new file mode 100644
index 0000000..9bcbd63
--- /dev/null
+++ b/tests/arithmetics/counters.js
@@ -0,0 +1,10 @@
+return new UnitTest('counters')
+    .add('postfix increment', function () { var i = 10; i++ === 10; })
+    .add('postfix decrement', function () { var i = 10; i-- === 10; })
+    .add('prefix decrement', function () { var i = 10; --i === 9; })
+    .add('prefix increment', function () { var i = 10; ++i === 11; })
+    .add('ostfix increment of non-number', function () { var i = 'hi mom'; isNaN(i++); })
+    .add('ostfix decrement of non-number', function () { var i = 'hi mom'; isNaN(i--); })
+    .add('prefix increment of non-number', function () { var i = 'hi mom'; isNaN(++i); })
+    .add('prefix decrement of non-number', function () { var i = 'hi mom'; isNaN(--i); })
+    .add('postfix increment of convertible to number', function () { var i = '10'; i++; i === 11; })
\ No newline at end of file
diff --git a/tests/arithmetics/index.js b/tests/arithmetics/index.js
new file mode 100644
index 0000000..a1cb82c
--- /dev/null
+++ b/tests/arithmetics/index.js
@@ -0,0 +1,2 @@
+return new UnitTest('Arithmetics')
+    .add(include('counters.js'))
\ No newline at end of file
diff --git a/tests/array/concat.js b/tests/array/concat.js
new file mode 100644
index 0000000..bab004f
--- /dev/null
+++ b/tests/array/concat.js
@@ -0,0 +1,4 @@
+return new UnitTest('concat', function() { return typeof Array.prototype.concat === 'function'; })
+    .add('two arrays', function() { return match([1, 2, 3], [1].concat([2], [3])) })
+    .add('simple spread', function() { return match([1, 2, 3, 4, 5], [1].concat([2], 3, [4, 5])) })
+    .add('sparse concat', function() { return match([1,, 2,,, 3,,, 4, 5], [1,,2].concat([,,3,,,4], 5)) })
\ No newline at end of file
diff --git a/tests/array/index.js b/tests/array/index.js
new file mode 100644
index 0000000..ee18fa2
--- /dev/null
+++ b/tests/array/index.js
@@ -0,0 +1,22 @@
+function runIterator(arr, method, func, n) {
+    var res = [];
+    var j = 1;
+    var args = [ function() {
+        var pushed = [];
+        for (var i = 0; i < n; i++) pushed[i] = arguments[i];
+        res[j++] = pushed;
+        return func.apply(this, arguments);
+    } ];
+
+    for (var i = 4; i < arguments.length; i++) args[i - 3] = arguments[i];
+
+    res[0] = method.apply(arr, args);
+
+    return res;
+}
+
+return new UnitTest('Array', function() { []; })
+    .add(include('length.js'))
+    .add(include('reduce.js'))
+    .add(include('sparse.js'))
+    .add(include('concat.js'))
diff --git a/tests/array/length.js b/tests/array/length.js
new file mode 100644
index 0000000..9bee0e1
--- /dev/null
+++ b/tests/array/length.js
@@ -0,0 +1,26 @@
+return new UnitTest('length & capacity', function() { return 'length' in Array.prototype; })
+    .add('empty literal', function() { return [].length === 0 })
+    .add('filled literal', function() { return [1, 2, 3].length === 3 })
+    .add('set length', function() {
+        var a = [];
+        a.length = 10;
+        return a.length === 10;
+    })
+    .add('length after set', function() {
+        var a = [];
+        a [5]= 5;
+        return a.length === 6;
+    })
+    .add('length after set (big', function() {
+        var a = [1, 2];
+        a [5000]= 5;
+        return a.length === 5001;
+    })
+    .add('expand test', function() {
+        var a = [];
+        for (var i = 0; i < 1000; i++) {
+            a[i] = i * 50;
+            if (a[i] !== i * 50) return false;
+        }
+        return a.length === 1000;
+    })
\ No newline at end of file
diff --git a/tests/array/reduce.js b/tests/array/reduce.js
new file mode 100644
index 0000000..c1c2892
--- /dev/null
+++ b/tests/array/reduce.js
@@ -0,0 +1,44 @@
+var res = [];
+
+return new UnitTest('reduceRight', function () { return typeof Array.prototype.reduceRight === 'function' })
+    .add('empty function', function () {match(
+        [ undefined, [4, 3, 2], [undefined, 2, 1], [undefined, 1, 0], ],
+        runIterator([1, 2, 3, 4], Array.prototype.reduceRight, function() { }, 3), 1
+    )})
+    .add('adder', function () {match(
+        [ 10, [4, 3, 2], [7, 2, 1], [9, 1, 0], ],
+        runIterator([1, 2, 3, 4], Array.prototype.reduceRight, function(a, b) { return a + b; }, 3), 1
+    )})
+    .add('sparse array', function () {match(
+        [ 10, [4, 3, 11], [7, 2, 7], [9, 1, 3], ],
+        runIterator([,,,1,,,, 2,,,, 3,,,, 4,,,,], Array.prototype.reduceRight, function(a, b) { return a + b }, 3), 1
+    )})
+    .add('sparse array with one element', function () {match(
+        [ 1 ],
+        runIterator([,,,1,,,,], Array.prototype.reduceRight, function(v) { return v; }, 3), 1
+    )})
+    .add('sparse array with no elements', function () {match(
+        [ undefined ],
+        runIterator([,,,,,,,], Array.prototype.reduceRight, function(v) { return v; }, 3), 1
+    )})
+
+    .add('initial value and empty function', function () {match(
+        [ undefined, [0, 4, 3], [undefined, 3, 2], [undefined, 2, 1], [undefined, 1, 0] ],
+        runIterator([1, 2, 3, 4], Array.prototype.reduceRight, function() { }, 3, 0), 1
+    )})
+    .add('initial value and adder', function () {match(
+        [ 15, [5, 4, 3], [9, 3, 2], [12, 2, 1], [14, 1, 0] ],
+        runIterator([1, 2, 3, 4], Array.prototype.reduceRight, function(a, b) { return a + b; }, 3, 5), 1
+    )})
+    .add('initial value, sparce array and adder', function () {match(
+        [ 15, [5, 4, 15], [9, 3, 11], [12, 2, 7], [14, 1, 3] ],
+        runIterator([,,,1,,,, 2,,,, 3,,,, 4,,,,], Array.prototype.reduceRight, function(a, b) { return a + b; }, 3, 5), 1
+    )})
+    .add('initial value and sparse array with one element', function () {match(
+        [ 6, [5, 1, 3] ],
+        runIterator([,,,1,,,,], Array.prototype.reduceRight, function(a, b) { return a + b; }, 3, 5), 1
+    )})
+    .add('initial value and sparse array with no elements', function () {match(
+        [ 5 ],
+        runIterator([,,,,,,,], Array.prototype.reduceRight, function(v) { return v; }, 3, 5), 1
+    )});
\ No newline at end of file
diff --git a/tests/array/sort.js b/tests/array/sort.js
new file mode 100644
index 0000000..bab004f
--- /dev/null
+++ b/tests/array/sort.js
@@ -0,0 +1,4 @@
+return new UnitTest('concat', function() { return typeof Array.prototype.concat === 'function'; })
+    .add('two arrays', function() { return match([1, 2, 3], [1].concat([2], [3])) })
+    .add('simple spread', function() { return match([1, 2, 3, 4, 5], [1].concat([2], 3, [4, 5])) })
+    .add('sparse concat', function() { return match([1,, 2,,, 3,,, 4, 5], [1,,2].concat([,,3,,,4], 5)) })
\ No newline at end of file
diff --git a/tests/array/sparse.js b/tests/array/sparse.js
new file mode 100644
index 0000000..ecd0e26
--- /dev/null
+++ b/tests/array/sparse.js
@@ -0,0 +1,5 @@
+return new UnitTest('sparse', function() { return !(0 in [,,]) })
+    .add('empty in start', function() { var a = [,1]; return !(0 in a) && (1 in a); })
+    .add('empty in middle', function() { var a = [1,,2]; return !(1 in a) && (2 in a) && (0 in a); })
+    .add('empty in end', function() { var a = [1,,]; return !(1 in a) && (0 in a); })
+    .add('trailing comma', function() { var a = [1,]; return a.length === 1; })
\ No newline at end of file
diff --git a/tests/index.js b/tests/index.js
new file mode 100644
index 0000000..6290b85
--- /dev/null
+++ b/tests/index.js
@@ -0,0 +1,70 @@
+function assert(cond, msg, locDepth) {
+    if (locDepth < 0 || locDepth === undefined) locDepth = 0;
+    if (!cond) {
+        log('Assert failed', (typeof locDepth === 'string' ? locDepth : Error().stack[locDepth + 1]) + ': ', msg);
+    }
+}
+function assertMatch(expected, actual, depth, msg) {
+    if (!match(expected, actual, depth)) {
+        log('Assert failed', Error().stack[1] + ': ', msg);
+        log('Expected:', expected);
+        log('Actual:', actual);
+    }
+}
+function match(expected, actual, depth) {
+    if (!Array.isArray(expected) || !Array.isArray(actual)) return expected === actual;
+    else if (expected.length !== actual.length) return false;
+    else if (depth === undefined || depth < 0) depth = 0;
+
+    for (var i = 0; i < expected.length; i++) {
+        if (!(i in expected) || !(i in actual)) return !(i in expected) && !(i in actual);
+
+        if (
+            expected[i] === actual[i] ||
+            depth > 0 &&
+            Array.isArray(expected) &&
+            Array.isArray(actual) &&
+            match(expected[i], actual[i], depth - 1)
+        ) continue;
+
+        return false;
+    }
+
+    return true;
+}
+
+/** @class */ function UnitTest(msg, exec) {
+    this.name = msg;
+    this.exec = exec;
+    this.subtests = [];
+}
+
+UnitTest.prototype.run = function(path) {
+    if (path === undefined) path = [];
+
+    path.push(this.name);
+
+    if (typeof this.exec === 'function') {
+        var res = true, err = 'exec() returned false.';
+        try {
+            if (this.exec() === false) res = false;
+        }
+        catch (e) { res = false; err = e; }
+        assert(res, path.join('/') + ': ' + err, this.exec.location());
+    }
+    for (var i = 0; i < this.subtests.length; i++) {
+        this.subtests[i].run(path);
+    }
+
+    path.pop();
+}
+UnitTest.prototype.add = function(test, exec) {
+    if (test instanceof UnitTest) this.subtests.push(test);
+    else this.subtests.push(new UnitTest(test, exec));
+    return this;
+}
+
+include('arithmetics/index.js').run();
+include('array/index.js').run();
+
+log('Tests complete.');
\ No newline at end of file