diff --git a/src/core/contains.js b/src/core/contains.js
index a650156..1e3d1fd 100644
--- a/src/core/contains.js
+++ b/src/core/contains.js
@@ -1,27 +1,41 @@
-const contains = (haystack, needle) => {
-  const needleType = typeof needle;
-  const haystackType = typeof haystack;
-  if (needleType !== haystackType) {
-    return false;
-  }
-  if (needleType === 'object') {
-    const needleIsArray = Array.isArray(needle);
-    const haystackIsArray = Array.isArray(haystack);
-    if (needleIsArray !== haystackIsArray) {
-      return false;
+const objectScan = require('object-scan');
+
+const scanner = objectScan(['**'], {
+  rtn: 'context',
+  abort: true,
+  breakFn: ({
+    isLeaf, isMatch, property, value, context
+  }) => {
+    const { stack } = context;
+    const last = stack[stack.length - 1];
+    if (isMatch && !(property in last)) {
+      context.result = false;
+      return true;
     }
-    // exact match for arrays
-    if (needleIsArray) {
-      if (needle.length !== haystack.length) {
-        return false;
+    const current = isMatch ? last[property] : last;
+    if (isLeaf) {
+      if (value !== current) {
+        context.result = false;
+        return true;
       }
-      return needle.every((e, idx) => contains(haystack[idx], e));
+    } else if (
+      value instanceof Object !== current instanceof Object
+      || Array.isArray(value) !== Array.isArray(current)
+      || (Array.isArray(value) && value.length !== current.length)
+    ) {
+      context.result = false;
+      return true;
     }
-    // subset match for object
-    return Object.keys(needle).every((key) => contains(haystack[key], needle[key]));
+    stack.push(current);
+    return false;
+  },
+  filterFn: ({ context }) => {
+    context.stack.pop();
+    return context.result !== true;
   }
-  // default comparison
-  return haystack === needle;
-};
+});
 
-module.exports = contains;
+module.exports = (tree, subtree) => {
+  const { result } = scanner(subtree, { stack: [tree], result: true });
+  return result;
+};
diff --git a/test/core/contains.spec.js b/test/core/contains.spec.js
index 33413d4..3151be5 100644
--- a/test/core/contains.spec.js
+++ b/test/core/contains.spec.js
@@ -1,29 +1,93 @@
 const expect = require('chai').expect;
+const { describe } = require('node-tdd');
 const contains = require('../../src/core/contains');
 
-describe('Testing contains', () => {
-  it('Testing String', () => {
-    expect(contains('value1', 'value1')).to.equal(true);
-    expect(contains('value1', 'value2')).to.equal(false);
+describe('Testing contains', { timeout: 100000 }, () => {
+  it('Batch test', ({ fixture }) => {
+    const gen = fixture('gen');
+    const containsRec = fixture('contains-rec');
+    for (let x = 0; x < 10000; x += 1) {
+      const tree = gen();
+      const subtree = gen();
+      expect(contains(tree, subtree)).to.equal(containsRec(tree, subtree));
+    }
   });
 
-  it('Testing List', () => {
-    expect(contains([1, 2, 3], [1, 2, 3])).to.equal(true);
-    expect(contains([{ key: 'value1' }], [{ key: 'value1' }])).to.equal(true);
-    expect(contains([{ key: 'value1' }], [{ key: 'value2' }])).to.equal(false);
-    expect(contains([1, 2, 3], [3, 2, 1])).to.equal(false);
-    expect(contains([1, 2, 3], [1, 2])).to.equal(false);
-    expect(contains([], [])).to.equal(true);
+  describe('Testing String', () => {
+    it('Testing equal', () => {
+      expect(contains('value1', 'value1')).to.equal(true);
+    });
+    it('Testing not equal', () => {
+      expect(contains('value1', 'value2')).to.equal(false);
+    });
   });
 
-  it('Testing Object', () => {
-    expect(contains({}, {})).to.equal(true);
-    expect(contains({ key: 'value1' }, { key: 'value1' })).to.equal(true);
-    expect(contains({ key: 'value1' }, { key: 'value2' })).to.equal(false);
+  describe('Testing Array', () => {
+    it('Testing equal arrays (containing three equal numbers)', () => {
+      expect(contains([1, 2, 3], [1, 2, 3])).to.equal(true);
+    });
+    it('Testing not equal arrays (containing three equal numbers in different order)', () => {
+      expect(contains([1, 2, 3], [3, 2, 1])).to.equal(false);
+    });
+    it('Testing equal arrays (containing single object)', () => {
+      expect(contains([{ key: 'value1' }], [{ key: 'value1' }])).to.equal(true);
+    });
+    it('Testing not equal arrays (containing different single object)', () => {
+      expect(contains([{ key: 'value1' }], [{ key: 'value2' }])).to.equal(false);
+    });
+    it('Testing not equal arrays (array contains number that are a subset)', () => {
+      expect(contains([1, 2, 3], [1, 2])).to.equal(false);
+    });
+    it('Testing empty arrays equal', () => {
+      expect(contains([], [])).to.equal(true);
+    });
+    it('Testing nested empty arrays equal', () => {
+      expect(contains([[], []], [[], []])).to.equal(true);
+    });
+    it('Testing nested not equal (different arrays, removed)', () => {
+      expect(contains([['x'], []], [[], []])).to.equal(false);
+    });
+    it('Testing nested not equal (different arrays, added)', () => {
+      expect(contains([[], []], [['x'], []])).to.equal(false);
+    });
   });
 
-  it('Testing Type Mismatch', () => {
-    expect(contains({}, '')).to.equal(false);
-    expect(contains({}, [])).to.equal(false);
+  describe('Testing Object', () => {
+    it('Testing empty objects equal', () => {
+      expect(contains({}, {})).to.equal(true);
+    });
+    it('Testing objects equal with single key', () => {
+      expect(contains({ key: 'value1' }, { key: 'value1' })).to.equal(true);
+    });
+    it('Testing objects different with same keys, but different values', () => {
+      expect(contains({ key: 'value1' }, { key: 'value2' })).to.equal(false);
+    });
+    it('Testing different keys (added)', () => {
+      expect(contains({ key: 'value1' }, { key: 'value1', foo: 'bar' })).to.equal(false);
+    });
+    it('Testing different keys (removed)', () => {
+      expect(contains({ key: 'value1', foo: 'bar' }, { key: 'value1' })).to.equal(true);
+    });
+  });
+
+  describe('Testing Type Mismatch', () => {
+    it('Testing empty object vs empty string', () => {
+      expect(contains({}, '')).to.equal(false);
+    });
+    it('Testing empty object vs empty array', () => {
+      expect(contains({}, [])).to.equal(false);
+    });
+    it('Testing empty array vs empty string', () => {
+      expect(contains([], '')).to.equal(false);
+    });
+    it('Testing empty array vs empty object', () => {
+      expect(contains([], {})).to.equal(false);
+    });
+    it('Testing empty string vs empty object', () => {
+      expect(contains('', {})).to.equal(false);
+    });
+    it('Testing empty string vs empty array', () => {
+      expect(contains('', [])).to.equal(false);
+    });
   });
 });
diff --git a/test/core/contains.spec.js__fixtures/contains-rec.js b/test/core/contains.spec.js__fixtures/contains-rec.js
new file mode 100644
index 0000000..f389647
--- /dev/null
+++ b/test/core/contains.spec.js__fixtures/contains-rec.js
@@ -0,0 +1,27 @@
+const containsRec = (haystack, needle) => {
+  const needleType = typeof needle;
+  const haystackType = typeof haystack;
+  if (needleType !== haystackType) {
+    return false;
+  }
+  if (needleType === 'object') {
+    const needleIsArray = Array.isArray(needle);
+    const haystackIsArray = Array.isArray(haystack);
+    if (needleIsArray !== haystackIsArray) {
+      return false;
+    }
+    // exact match for arrays
+    if (needleIsArray) {
+      if (needle.length !== haystack.length) {
+        return false;
+      }
+      return needle.every((e, idx) => containsRec(haystack[idx], e));
+    }
+    // subset match for object
+    return Object.keys(needle).every((key) => containsRec(haystack[key], needle[key]));
+  }
+  // default comparison
+  return haystack === needle;
+};
+
+module.exports = containsRec;
diff --git a/test/core/contains.spec.js__fixtures/gen.js b/test/core/contains.spec.js__fixtures/gen.js
new file mode 100644
index 0000000..58246ab
--- /dev/null
+++ b/test/core/contains.spec.js__fixtures/gen.js
@@ -0,0 +1,18 @@
+const rand = (values) => Math.floor(Math.random() * values);
+
+const gen = (depth) => {
+  const v = rand(3);
+  if (v === 0 || depth >= 3) {
+    return rand(3);
+  }
+  if (v === 1) {
+    return Array.from({ length: rand(3) }, () => gen(depth + 1));
+  }
+  const r = {};
+  for (let idx = 0, len = gen(3) + 1; idx < len; idx += 1) {
+    r[['A', 'B', 'C'][idx]] = gen(depth + 1);
+  }
+  return r;
+};
+
+module.exports = () => gen(0);