diff --git a/sampling/sampler.py b/sampling/sampler.py
index 2950557..1a819bc 100644
--- a/sampling/sampler.py
+++ b/sampling/sampler.py
@@ -280,6 +280,10 @@ def single_chain_sample(self, num_steps, x_initial, random_key, output, thinning
             return self.sample_expectation(num_steps, x, u, l, g, key, L, eps, sigma)
 
         elif output == 'ess':
+            try:
+                self.Target.variance
+            except:
+                raise AttributeError("Target.variance should be defined")
             return self.sample_ess(num_steps, x, u, l, g, key, L, eps, sigma)
 
         else:
diff --git a/tests/test_mclmc.py b/tests/test_mclmc.py
index fd75b01..f312b33 100644
--- a/tests/test_mclmc.py
+++ b/tests/test_mclmc.py
@@ -1,4 +1,7 @@
-import sys  
+import sys
+
+from pytest import raises
+import pytest  
 sys.path.insert(0, '../../')
 sys.path.insert(0, './')
 
@@ -25,18 +28,47 @@ def prior_draw(self, key):
 
     return jax.random.normal(key, shape = (self.d, ), dtype = 'float64') * 4
 
-target = StandardGaussian(d = 10, nlogp=nlogp)
-sampler = Sampler(target, varEwanted = 5e-4)
 
-target_simple = Target(d = 10, nlogp=nlogp)
 
 def test_mclmc():
+    target = StandardGaussian(d = 10, nlogp=nlogp)
+    sampler = Sampler(target, varEwanted = 5e-4)
+
+
     samples1 = sampler.sample(100, 1, random_key=jax.random.PRNGKey(0))
     samples2 = sampler.sample(100, 1, random_key=jax.random.PRNGKey(0))
     samples3 = sampler.sample(100, 1, random_key=jax.random.PRNGKey(1))
     assert jnp.array_equal(samples1,samples2), "sampler should be pure"
     assert not jnp.array_equal(samples1,samples3), "this suggests that seed is not being used"
+    # run without key
+    sampler.sample(20)
     # run with multiple chains
-    sampler.sample(100, 3)
+    sampler.sample(20, 3)
+    # run with different output types
+    sampler.sample(20, 3, output='expectation')
+    sampler.sample(20, 3, output='detailed')
+    sampler.sample(20, 3, output='normal')
+
+    with raises(AttributeError) as excinfo:
+        sampler.sample(20, 3, output='ess')
+
+    # run with leapfrog
+    sampler = Sampler(target, varEwanted = 5e-4, integrator='LF')
+    sampler.sample(20)
+    # run without autotune
+    sampler = Sampler(target, varEwanted = 5e-4, frac_tune1 = 0.1, frac_tune2 = 0.1, frac_tune3 = 0.1,)
+    sampler.sample(20,)
 
+    # with a specific initial point
+    sampler.sample(20, x_initial=jax.random.normal(shape=(10,), key=jax.random.PRNGKey(0)))
+    
+    # running with wrong dimensions causes TypeError
+    with raises(TypeError) as excinfo:  
+        sampler.sample(20, x_initial=jax.random.normal(shape=(11,), key=jax.random.PRNGKey(0)))
+    
+    # multiple chains
+    sampler.sample(20, 3)
+    
+    # simple target
+    target_simple = Target(d = 10, nlogp=nlogp)
     Sampler(target_simple).sample(100, x_initial = jax.random.normal(shape=(10,), key=jax.random.PRNGKey(0)))