diff --git a/package.json b/package.json
index d84013c..2535a39 100644
--- a/package.json
+++ b/package.json
@@ -4,7 +4,8 @@
   "description": "JSON Web Token implementation (symmetric and asymmetric)",
   "main": "index.js",
   "scripts": {
-    "test": "nyc --reporter=html --reporter=text mocha && nsp check && cost-of-modules"
+    "test:unit": "nyc --reporter=html --reporter=text mocha",
+    "test": "npm run test:unit && nsp check && cost-of-modules"
   },
   "repository": {
     "type": "git",
diff --git a/test/iat.tests.js b/test/iat.tests.js
index 00647f1..953bdb3 100644
--- a/test/iat.tests.js
+++ b/test/iat.tests.js
@@ -12,13 +12,4 @@ describe('iat', function () {
     expect(result.exp).to.be.closeTo(iat + expiresIn, 0.2);
   });
 
-  it('should work with a nbf calculated based on numeric iat', function () {
-    var dateNow = Math.floor(Date.now() / 1000);
-    var iat = dateNow - 30;
-    var notBefore = -50;
-    var token = jwt.sign({foo: 123, iat: iat}, '123', {notBefore: notBefore});
-    var result = jwt.verify(token, '123');
-    expect(result.nbf).to.equal(iat + notBefore);
-  });
-
 });
diff --git a/test/jwt.asymmetric_signing.tests.js b/test/jwt.asymmetric_signing.tests.js
index 287a233..8fd612f 100644
--- a/test/jwt.asymmetric_signing.tests.js
+++ b/test/jwt.asymmetric_signing.tests.js
@@ -114,57 +114,6 @@ describe('Asymmetric Algorithms', function(){
         });
       });
 
-      describe('when signing a token with not before', function () {
-        var token = jwt.sign({ foo: 'bar' }, priv, { algorithm: algorithm, notBefore: -10 * 3600 });
-
-        it('should be valid expiration', function (done) {
-          jwt.verify(token, pub, function (err, decoded) {
-            assert.isNotNull(decoded);
-            assert.isNull(err);
-            done();
-          });
-        });
-
-        it('should be invalid', function (done) {
-          // not active token
-          token = jwt.sign({ foo: 'bar' }, priv, { algorithm: algorithm, notBefore: '10m' });
-
-          jwt.verify(token, pub, function (err, decoded) {
-            assert.isUndefined(decoded);
-            assert.isNotNull(err);
-            assert.equal(err.name, 'NotBeforeError');
-            assert.instanceOf(err.date, Date);
-            assert.instanceOf(err, jwt.NotBeforeError);
-            done();
-          });
-        });
-
-
-        it('should valid when date are equals', function (done) {
-          var fakeClock = sinon.useFakeTimers({now: 1451908031});
-
-          token = jwt.sign({ foo: 'bar' }, priv, { algorithm: algorithm, notBefore: 0 });
-
-          jwt.verify(token, pub, function (err, decoded) {
-            fakeClock.uninstall();
-            assert.isNull(err);
-            assert.isNotNull(decoded);
-            done();
-          });
-        });
-
-        it('should NOT be invalid', function (done) {
-          // not active token
-          token = jwt.sign({ foo: 'bar' }, priv, { algorithm: algorithm, notBefore: '10m' });
-
-          jwt.verify(token, pub, { ignoreNotBefore: true }, function (err, decoded) {
-            assert.ok(decoded.foo);
-            assert.equal('bar', decoded.foo);
-            done();
-          });
-        });
-      });
-
       describe('when signing a token with audience', function () {
         var token = jwt.sign({ foo: 'bar' }, priv, { algorithm: algorithm, audience: 'urn:foo' });
 
diff --git a/test/nbf.test.js b/test/nbf.test.js
new file mode 100644
index 0000000..5c4d898
--- /dev/null
+++ b/test/nbf.test.js
@@ -0,0 +1,257 @@
+'use strict';
+
+const jwt = require('../');
+const expect = require('chai').expect;
+const sinon = require('sinon');
+const util = require('util');
+
+function base64UrlEncode(str) {
+  return Buffer.from(str).toString('base64')
+    .replace(/=/g, "")
+    .replace(/\+/g, "-")
+    .replace(/\//g, "_")
+  ;
+}
+
+function signWithNoBefore(payload, notBefore) {
+  const options = {algorithm: 'none'};
+  if (notBefore !== undefined) {
+    options.notBefore = notBefore;
+  }
+  return jwt.sign(payload, undefined, options);
+}
+
+const noneAlgorithmHeader = 'eyJhbGciOiJub25lIiwidHlwIjoiSldUIn0';
+
+describe('not before', function() {
+  describe('`jwt.sign` notBefore option validation', function () {
+    [
+      true,
+      false,
+      null,
+      -1.1,
+      1.1,
+      -Infinity,
+      Infinity,
+      NaN,
+      // TODO empty string currently fails
+      // '',
+      ' ',
+      'invalid',
+      [],
+      ['foo'],
+      {},
+      {foo: 'bar'},
+    ].forEach((notBefore) => {
+      it(`should error with with value ${util.inspect(notBefore)}`, function () {
+        expect(() => signWithNoBefore({}, notBefore)).to.throw(
+          '"notBefore" should be a number of seconds or string representing a timespan'
+        );
+      });
+    });
+
+    // undefined needs special treatment because {} is not the same as {notBefore: undefined}
+    it('should error with with value undefined', function () {
+      expect(() =>jwt.sign({}, undefined, {notBefore: undefined, algorithm: 'none'})).to.throw(
+        '"notBefore" should be a number of seconds or string representing a timespan'
+      );
+    });
+
+    it ('should error when "nbf" is in payload', function() {
+      expect(() => signWithNoBefore({nbf: 100}, 100)).to.throw(
+        'Bad "options.notBefore" option the payload already has an "nbf" property.'
+      );
+    });
+
+    it('should error with a string payload', function() {
+      expect(() => signWithNoBefore('a string payload', 100)).to.throw(
+        'invalid notBefore option for string payload'
+      );
+    });
+
+    it('should error with a Buffer payload', function() {
+      expect(() => signWithNoBefore(new Buffer('a Buffer payload'), 100)).to.throw(
+        'invalid notBefore option for object payload'
+      );
+    });
+  });
+
+  describe('`jwt.sign` nbf claim validation', function () {
+    [
+      true,
+      false,
+      null,
+      undefined,
+      // TODO should these fail in validation?
+      // -Infinity,
+      // Infinity,
+      // NaN,
+      '',
+      ' ',
+      'invalid',
+      [],
+      ['foo'],
+      {},
+      {foo: 'bar'},
+    ].forEach((nbf) => {
+      it(`should error with with value ${util.inspect(nbf)}`, function () {
+        expect(() => signWithNoBefore({nbf})).to.throw(
+          '"nbf" should be a number of seconds'
+        );
+      });
+    });
+  });
+
+  describe('nbf in payload validation', function () {
+    [
+      true,
+      false,
+      null,
+      -Infinity,
+      Infinity,
+      NaN,
+      '',
+      ' ',
+      'invalid',
+      [],
+      ['foo'],
+      {},
+      {foo: 'bar'},
+    ].forEach((nbf) => {
+      it(`should error with with value ${util.inspect(nbf)}`, function () {
+        const encodedPayload = base64UrlEncode(JSON.stringify({nbf}));
+        const token = `${noneAlgorithmHeader}.${encodedPayload}.`;
+        expect(() => jwt.verify(token, undefined)).to.throw(
+          jwt.JsonWebTokenError,
+          'invalid nbf value'
+        );
+      });
+    })
+  });
+
+  describe('when signing and verifying a token with notBefore option', function () {
+    let fakeClock;
+    beforeEach(function() {
+      fakeClock = sinon.useFakeTimers({now: 60000});
+    });
+
+    afterEach(function() {
+      fakeClock.uninstall();
+    });
+
+
+    it('should set correct "nbf" with negative number of seconds', function() {
+      const token = signWithNoBefore({}, -10);
+      const decoded = jwt.decode(token);
+
+      const verified = jwt.verify(token, undefined);
+      expect(decoded).to.deep.equal(verified);
+      expect(decoded.nbf).to.equal(50);
+    });
+
+    it('should set correct "nbf" with positive number of seconds', function() {
+      const token = signWithNoBefore({}, 10);
+
+      fakeClock.tick(10000);
+      const decoded = jwt.decode(token);
+
+      const verified = jwt.verify(token, undefined);
+      expect(decoded).to.deep.equal(verified);
+      expect(decoded.nbf).to.equal(70);
+    });
+
+    it('should set correct "nbf" with zero seconds', function() {
+      const token = signWithNoBefore({}, 0);
+
+      const decoded = jwt.decode(token);
+
+      const verified = jwt.verify(token, undefined);
+      expect(decoded).to.deep.equal(verified);
+      expect(decoded.nbf).to.equal(60);
+    });
+
+    it('should set correct "nbf" with negative string timespan', function() {
+      const token = signWithNoBefore({}, '-10 s');
+
+      const decoded = jwt.decode(token);
+
+      const verified = jwt.verify(token, undefined);
+      expect(decoded).to.deep.equal(verified);
+      expect(decoded.nbf).to.equal(50);
+    });
+
+
+    it('should set correct "nbf" with positive string timespan', function() {
+      const token = signWithNoBefore({}, '10 s');
+
+      fakeClock.tick(10000);
+      const decoded = jwt.decode(token);
+
+      const verified = jwt.verify(token, undefined);
+      expect(decoded).to.deep.equal(verified);
+      expect(decoded.nbf).to.equal(70);
+    });
+
+    it('should set correct "nbf" with zero string timespan', function() {
+      const token = signWithNoBefore({}, '0 s');
+
+      const decoded = jwt.decode(token);
+
+      const verified = jwt.verify(token, undefined);
+      expect(decoded).to.deep.equal(verified);
+      expect(decoded.nbf).to.equal(60);
+    });
+
+    it('should set correct "nbf" when "iat" is passed', function () {
+      const token = signWithNoBefore({iat: 40}, -10);
+
+      const decoded = jwt.decode(token);
+
+      const verified = jwt.verify(token, undefined);
+      expect(decoded).to.deep.equal(verified);
+      expect(decoded.nbf).to.equal(30);
+    });
+
+    it('should verify "nbf" using "clockTimestamp"', function () {
+      const token = signWithNoBefore({}, 10);
+
+      const verified = jwt.verify(token, undefined, {clockTimestamp: 70});
+      expect(verified.iat).to.equal(60);
+      expect(verified.nbf).to.equal(70);
+    });
+
+    it('should verify "nbf" using "clockTolerance"', function () {
+      const token = signWithNoBefore({}, 5);
+
+      const verified = jwt.verify(token, undefined, {clockTolerance: 6});
+      expect(verified.iat).to.equal(60);
+      expect(verified.nbf).to.equal(65);
+    });
+
+    it('should ignore a not active token when "ignoreNotBefore" is true', function () {
+      const token = signWithNoBefore({}, '10 s');
+
+      const verified = jwt.verify(token, undefined, {ignoreNotBefore: true});
+      expect(verified.iat).to.equal(60);
+      expect(verified.nbf).to.equal(70);
+    });
+
+    it('should error on verify if "nbf" is after current time', function() {
+      const token = signWithNoBefore({nbf: 61});
+
+      expect(() => jwt.verify(token, undefined)).to.throw(
+        jwt.NotBeforeError,
+        'jwt not active'
+      );
+    });
+
+    it('should error on verify if "nbf" is after current time using clockTolerance', function () {
+      const token = signWithNoBefore({}, 5);
+
+      expect(() => jwt.verify(token, undefined, {clockTolerance: 4})).to.throw(
+        jwt.NotBeforeError,
+        'jwt not active'
+      );
+    });
+  });
+});
\ No newline at end of file
diff --git a/test/schema.tests.js b/test/schema.tests.js
index 1f79994..a6a9128 100644
--- a/test/schema.tests.js
+++ b/test/schema.tests.js
@@ -25,17 +25,6 @@ describe('schema', function() {
       sign({ expiresIn: 10 });
     });
 
-    it('should validate notBefore', function () {
-      expect(function () {
-        sign({ notBefore: '1 monkey' });
-      }).to.throw(/"notBefore" should be a number of seconds or string representing a timespan/);
-      expect(function () {
-        sign({ notBefore: 1.1 });
-      }).to.throw(/"notBefore" should be a number of seconds or string representing a timespan/);
-      sign({ notBefore: '10s' });
-      sign({ notBefore: 10 });
-    });
-
     it('should validate audience', function () {
       expect(function () {
         sign({ audience: 10 });
@@ -124,13 +113,6 @@ describe('schema', function() {
       sign({ exp: 10.1 });
     });
 
-    it('should validate nbf', function () {
-      expect(function () {
-        sign({ nbf: '1 monkey' });
-      }).to.throw(/"nbf" should be a number of seconds/);
-      sign({ nbf: 10.1 });
-    });
-
   });
 
 });
\ No newline at end of file
diff --git a/test/verify.tests.js b/test/verify.tests.js
index 51d107e..3d728ac 100644
--- a/test/verify.tests.js
+++ b/test/verify.tests.js
@@ -333,33 +333,6 @@ describe('verify', function() {
           done();
         });
       });
-      it('should verify valid token with nbf', function (done) {
-        var token = jwt.sign({
-          foo: 'bar',
-          iat: clockTimestamp,
-          nbf: clockTimestamp + 1,
-          exp: clockTimestamp + 2
-        }, key);
-        jwt.verify(token, key, {clockTimestamp: clockTimestamp + 1}, function (err, p) {
-          assert.isNull(err);
-          done();
-        });
-      });
-      it('should error on token used before nbf', function (done) {
-        var token = jwt.sign({
-          foo: 'bar',
-          iat: clockTimestamp,
-          nbf: clockTimestamp + 1,
-          exp: clockTimestamp + 2
-        }, key);
-        jwt.verify(token, key, {clockTimestamp: clockTimestamp}, function (err, p) {
-          assert.equal(err.name, 'NotBeforeError');
-          assert.equal(err.date.constructor.name, 'Date');
-          assert.equal(Number(err.date), (clockTimestamp + 1) * 1000);
-          assert.isUndefined(p);
-          done();
-        });
-      });
     });
 
     describe('option: maxAge and clockTimestamp', function () {