diff --git a/tests/phase0/block_processing/test_process_attester_slashing.py b/tests/phase0/block_processing/test_process_attester_slashing.py
new file mode 100644
index 000000000..ed6d9adae
--- /dev/null
+++ b/tests/phase0/block_processing/test_process_attester_slashing.py
@@ -0,0 +1,97 @@
+from copy import deepcopy
+import pytest
+
+import build.phase0.spec as spec
+from build.phase0.spec import (
+    get_balance,
+    get_current_epoch,
+    process_attester_slashing,
+)
+from tests.phase0.helpers import (
+    get_valid_attester_slashing,
+)
+
+# mark entire file as 'attester_slashing'
+pytestmark = pytest.mark.attester_slashings
+
+
+def run_attester_slashing_processing(state, attester_slashing, valid=True):
+    """
+    Run ``process_attester_slashing`` returning the pre and post state.
+    If ``valid == False``, run expecting ``AssertionError``
+    """
+    post_state = deepcopy(state)
+
+    if not valid:
+        with pytest.raises(AssertionError):
+            process_attester_slashing(post_state, attester_slashing)
+        return state, None
+
+    process_attester_slashing(post_state, attester_slashing)
+
+    validator_index = attester_slashing.attestation_1.custody_bit_0_indices[0]
+    slashed_validator = post_state.validator_registry[validator_index]
+    assert not slashed_validator.initiated_exit
+    assert slashed_validator.slashed
+    assert slashed_validator.exit_epoch < spec.FAR_FUTURE_EPOCH
+    assert slashed_validator.withdrawable_epoch < spec.FAR_FUTURE_EPOCH
+    # lost whistleblower reward
+    assert (
+        get_balance(post_state, validator_index) <
+        get_balance(state, validator_index)
+    )
+
+    return state, post_state
+
+
+def test_success_double(state):
+    attester_slashing = get_valid_attester_slashing(state)
+
+    pre_state, post_state = run_attester_slashing_processing(state, attester_slashing)
+
+    return pre_state, attester_slashing, post_state
+
+
+def test_success_surround(state):
+    attester_slashing = get_valid_attester_slashing(state)
+
+    # set attestion1 to surround attestation 2
+    attester_slashing.attestation_1.data.source_epoch = attester_slashing.attestation_2.data.source_epoch - 1
+    attester_slashing.attestation_1.data.slot = attester_slashing.attestation_2.data.slot + spec.SLOTS_PER_EPOCH
+
+    pre_state, post_state = run_attester_slashing_processing(state, attester_slashing)
+
+    return pre_state, attester_slashing, post_state
+
+
+def test_same_data(state):
+    attester_slashing = get_valid_attester_slashing(state)
+
+    attester_slashing.attestation_1.data = attester_slashing.attestation_2.data
+
+    pre_state, post_state = run_attester_slashing_processing(state, attester_slashing, False)
+
+    return pre_state, attester_slashing, post_state
+
+
+def test_no_double_or_surround(state):
+    attester_slashing = get_valid_attester_slashing(state)
+
+    attester_slashing.attestation_1.data.slot += spec.SLOTS_PER_EPOCH
+
+    pre_state, post_state = run_attester_slashing_processing(state, attester_slashing, False)
+
+    return pre_state, attester_slashing, post_state
+
+def test_participants_already_slashed(state):
+    attester_slashing = get_valid_attester_slashing(state)
+
+    # set all indices to slashed
+    attestation_1 = attester_slashing.attestation_1
+    validator_indices = attestation_1.custody_bit_0_indices + attestation_1.custody_bit_1_indices
+    for index in validator_indices:
+        state.validator_registry[index].slashed = True
+
+    pre_state, post_state = run_attester_slashing_processing(state, attester_slashing, False)
+
+    return pre_state, attester_slashing, post_state