diff --git a/tests/core/pyspec/eth2spec/test/fork_choice/test_on_attestation.py b/tests/core/pyspec/eth2spec/test/fork_choice/test_on_attestation.py
index 09248944c..265e8769a 100644
--- a/tests/core/pyspec/eth2spec/test/fork_choice/test_on_attestation.py
+++ b/tests/core/pyspec/eth2spec/test/fork_choice/test_on_attestation.py
@@ -1,4 +1,4 @@
-from eth2spec.test.context import with_all_phases, spec_state_test
+from eth2spec.test.context import PHASE0, with_all_phases, spec_state_test
 from eth2spec.test.helpers.block import build_empty_block_for_next_slot
 from eth2spec.test.helpers.attestations import get_valid_attestation, sign_attestation
 from eth2spec.test.helpers.state import transition_to, state_transition_and_sign_block
@@ -16,7 +16,7 @@ def run_on_attestation(spec, state, store, attestation, valid=True):
     indexed_attestation = spec.get_indexed_attestation(state, attestation)
     spec.on_attestation(store, attestation)
 
-    if spec.fork == 'phase0':
+    if spec.fork == PHASE0:
         sample_index = indexed_attestation.attesting_indices[0]
     else:
         attesting_indices = [
diff --git a/tests/core/pyspec/eth2spec/test/genesis/test_initialization.py b/tests/core/pyspec/eth2spec/test/genesis/test_initialization.py
index 61a2ffb1e..882821337 100644
--- a/tests/core/pyspec/eth2spec/test/genesis/test_initialization.py
+++ b/tests/core/pyspec/eth2spec/test/genesis/test_initialization.py
@@ -1,10 +1,10 @@
-from eth2spec.test.context import spec_test, with_phases, single_phase
+from eth2spec.test.context import PHASE0, spec_test, with_phases, single_phase
 from eth2spec.test.helpers.deposits import (
     prepare_genesis_deposits,
 )
 
 
-@with_phases(['phase0'])
+@with_phases(([PHASE0]))
 @spec_test
 @single_phase
 def test_initialize_beacon_state_from_eth1(spec):
@@ -32,7 +32,7 @@ def test_initialize_beacon_state_from_eth1(spec):
     yield 'state', state
 
 
-@with_phases(['phase0'])
+@with_phases([PHASE0])
 @spec_test
 @single_phase
 def test_initialize_beacon_state_some_small_balances(spec):
diff --git a/tests/core/pyspec/eth2spec/test/genesis/test_validity.py b/tests/core/pyspec/eth2spec/test/genesis/test_validity.py
index a90b4a695..dbaf3f951 100644
--- a/tests/core/pyspec/eth2spec/test/genesis/test_validity.py
+++ b/tests/core/pyspec/eth2spec/test/genesis/test_validity.py
@@ -1,4 +1,4 @@
-from eth2spec.test.context import spec_test, with_phases, single_phase
+from eth2spec.test.context import PHASE0, spec_test, with_phases, single_phase
 from eth2spec.test.helpers.deposits import (
     prepare_genesis_deposits,
 )
@@ -25,7 +25,7 @@ def run_is_valid_genesis_state(spec, state, valid=True):
     assert is_valid == valid
 
 
-@with_phases(['phase0'])
+@with_phases([PHASE0])
 @spec_test
 @single_phase
 def test_is_valid_genesis_state_true(spec):
@@ -34,7 +34,7 @@ def test_is_valid_genesis_state_true(spec):
     yield from run_is_valid_genesis_state(spec, state, valid=True)
 
 
-@with_phases(['phase0'])
+@with_phases([PHASE0])
 @spec_test
 @single_phase
 def test_is_valid_genesis_state_false_invalid_timestamp(spec):
@@ -44,7 +44,7 @@ def test_is_valid_genesis_state_false_invalid_timestamp(spec):
     yield from run_is_valid_genesis_state(spec, state, valid=False)
 
 
-@with_phases(['phase0'])
+@with_phases([PHASE0])
 @spec_test
 @single_phase
 def test_is_valid_genesis_state_true_more_balance(spec):
@@ -55,7 +55,7 @@ def test_is_valid_genesis_state_true_more_balance(spec):
 
 
 # TODO: not part of the genesis function yet. Erroneously merged.
-# @with_phases(['phase0'])
+# @with_phases([PHASE0])
 # @spec_test
 # def test_is_valid_genesis_state_false_not_enough_balance(spec):
 #     state = create_valid_beacon_state(spec)
@@ -64,7 +64,7 @@ def test_is_valid_genesis_state_true_more_balance(spec):
 #     yield from run_is_valid_genesis_state(spec, state, valid=False)
 
 
-@with_phases(['phase0'])
+@with_phases([PHASE0])
 @spec_test
 @single_phase
 def test_is_valid_genesis_state_true_one_more_validator(spec):
@@ -78,7 +78,7 @@ def test_is_valid_genesis_state_true_one_more_validator(spec):
     yield from run_is_valid_genesis_state(spec, state, valid=True)
 
 
-@with_phases(['phase0'])
+@with_phases([PHASE0])
 @spec_test
 @single_phase
 def test_is_valid_genesis_state_false_not_enough_validator(spec):
diff --git a/tests/core/pyspec/eth2spec/test/helpers/attestations.py b/tests/core/pyspec/eth2spec/test/helpers/attestations.py
index 281d11b45..4581af24e 100644
--- a/tests/core/pyspec/eth2spec/test/helpers/attestations.py
+++ b/tests/core/pyspec/eth2spec/test/helpers/attestations.py
@@ -1,5 +1,6 @@
 from typing import List
 
+from eth2spec.test.context import PHASE0
 from eth2spec.test.helpers.block import build_empty_block_for_next_slot, transition_unsigned_block, \
     build_empty_block
 from eth2spec.test.helpers.keys import privkeys
@@ -78,12 +79,12 @@ def sign_aggregate_attestation(spec, state, attestation_data, participants: List
                 privkey
             )
         )
-    # TODO: we should try signing custody bits if spec.fork == 'phase1'
+    # TODO: we should try signing custody bits if spec.fork == PHASE1
     return bls.Aggregate(signatures)
 
 
 def sign_indexed_attestation(spec, state, indexed_attestation):
-    if spec.fork == 'phase0':
+    if spec.fork == PHASE0:
         participants = indexed_attestation.attesting_indices
         data = indexed_attestation.data
         indexed_attestation.signature = sign_aggregate_attestation(spec, state, data, participants)
diff --git a/tests/core/pyspec/eth2spec/test/helpers/attester_slashings.py b/tests/core/pyspec/eth2spec/test/helpers/attester_slashings.py
index 5dfedc200..975f34c20 100644
--- a/tests/core/pyspec/eth2spec/test/helpers/attester_slashings.py
+++ b/tests/core/pyspec/eth2spec/test/helpers/attester_slashings.py
@@ -1,3 +1,4 @@
+from eth2spec.test.context import PHASE1
 from eth2spec.test.helpers.attestations import get_valid_attestation, sign_attestation
 
 
@@ -20,7 +21,7 @@ def get_indexed_attestation_participants(spec, indexed_att):
     """
     Wrapper around index-attestation to return the list of participant indices, regardless of spec phase.
     """
-    if spec.fork == "phase1":
+    if spec.fork == PHASE1:
         return list(spec.get_indices_from_committee(
             indexed_att.committee,
             indexed_att.attestation.aggregation_bits,
@@ -33,21 +34,21 @@ def set_indexed_attestation_participants(spec, indexed_att, participants):
     """
     Wrapper around index-attestation to return the list of participant indices, regardless of spec phase.
     """
-    if spec.fork == "phase1":
+    if spec.fork == PHASE1:
         indexed_att.attestation.aggregation_bits = [bool(i in participants) for i in indexed_att.committee]
     else:
         indexed_att.attesting_indices = participants
 
 
 def get_attestation_1_data(spec, att_slashing):
-    if spec.fork == "phase1":
+    if spec.fork == PHASE1:
         return att_slashing.attestation_1.attestation.data
     else:
         return att_slashing.attestation_1.data
 
 
 def get_attestation_2_data(spec, att_slashing):
-    if spec.fork == "phase1":
+    if spec.fork == PHASE1:
         return att_slashing.attestation_2.attestation.data
     else:
         return att_slashing.attestation_2.data
diff --git a/tests/core/pyspec/eth2spec/test/phase_0/block_processing/test_process_attester_slashing.py b/tests/core/pyspec/eth2spec/test/phase_0/block_processing/test_process_attester_slashing.py
index e9665e714..48dc75fd9 100644
--- a/tests/core/pyspec/eth2spec/test/phase_0/block_processing/test_process_attester_slashing.py
+++ b/tests/core/pyspec/eth2spec/test/phase_0/block_processing/test_process_attester_slashing.py
@@ -1,4 +1,7 @@
-from eth2spec.test.context import spec_state_test, expect_assertion_error, always_bls, with_all_phases, with_phases
+from eth2spec.test.context import (
+    PHASE0, PHASE1,
+    spec_state_test, expect_assertion_error, always_bls, with_all_phases, with_phases
+)
 from eth2spec.test.helpers.attestations import sign_indexed_attestation
 from eth2spec.test.helpers.attester_slashings import get_valid_attester_slashing, \
     get_indexed_attestation_participants, get_attestation_2_data, get_attestation_1_data
@@ -161,7 +164,7 @@ def test_same_data(spec, state):
 
     indexed_att_1 = attester_slashing.attestation_1
     att_2_data = get_attestation_2_data(spec, attester_slashing)
-    if spec.fork == 'phase1':
+    if spec.fork == PHASE1:
         indexed_att_1.attestation.data = att_2_data
     else:
         indexed_att_1.data = att_2_data
@@ -199,7 +202,7 @@ def test_participants_already_slashed(spec, state):
 # Some of the following tests are phase0 only: phase 1 lists participants with bitfields instead of index list.
 
 
-@with_phases(['phase0'])
+@with_phases([PHASE0])
 @spec_state_test
 @always_bls
 def test_att1_bad_extra_index(spec, state):
@@ -215,7 +218,7 @@ def test_att1_bad_extra_index(spec, state):
     yield from run_attester_slashing_processing(spec, state, attester_slashing, False)
 
 
-@with_phases(['phase0'])
+@with_phases([PHASE0])
 @spec_state_test
 @always_bls
 def test_att1_bad_replaced_index(spec, state):
@@ -231,7 +234,7 @@ def test_att1_bad_replaced_index(spec, state):
     yield from run_attester_slashing_processing(spec, state, attester_slashing, False)
 
 
-@with_phases(['phase0'])
+@with_phases([PHASE0])
 @spec_state_test
 @always_bls
 def test_att2_bad_extra_index(spec, state):
@@ -247,7 +250,7 @@ def test_att2_bad_extra_index(spec, state):
     yield from run_attester_slashing_processing(spec, state, attester_slashing, False)
 
 
-@with_phases(['phase0'])
+@with_phases([PHASE0])
 @spec_state_test
 @always_bls
 def test_att2_bad_replaced_index(spec, state):
@@ -263,7 +266,7 @@ def test_att2_bad_replaced_index(spec, state):
     yield from run_attester_slashing_processing(spec, state, attester_slashing, False)
 
 
-@with_phases(['phase0'])
+@with_phases([PHASE0])
 @spec_state_test
 @always_bls
 def test_att1_duplicate_index_normal_signed(spec, state):
@@ -283,7 +286,7 @@ def test_att1_duplicate_index_normal_signed(spec, state):
     yield from run_attester_slashing_processing(spec, state, attester_slashing, False)
 
 
-@with_phases(['phase0'])
+@with_phases([PHASE0])
 @spec_state_test
 @always_bls
 def test_att2_duplicate_index_normal_signed(spec, state):
@@ -303,7 +306,7 @@ def test_att2_duplicate_index_normal_signed(spec, state):
     yield from run_attester_slashing_processing(spec, state, attester_slashing, False)
 
 
-@with_phases(['phase0'])
+@with_phases([PHASE0])
 @spec_state_test
 @always_bls
 def test_att1_duplicate_index_double_signed(spec, state):
@@ -318,7 +321,7 @@ def test_att1_duplicate_index_double_signed(spec, state):
     yield from run_attester_slashing_processing(spec, state, attester_slashing, False)
 
 
-@with_phases(['phase0'])
+@with_phases([PHASE0])
 @spec_state_test
 @always_bls
 def test_att2_duplicate_index_double_signed(spec, state):
@@ -333,7 +336,7 @@ def test_att2_duplicate_index_double_signed(spec, state):
     yield from run_attester_slashing_processing(spec, state, attester_slashing, False)
 
 
-@with_phases(['phase0'])
+@with_phases([PHASE0])
 @spec_state_test
 def test_unsorted_att_1(spec, state):
     attester_slashing = get_valid_attester_slashing(spec, state, signed_1=False, signed_2=True)
@@ -346,7 +349,7 @@ def test_unsorted_att_1(spec, state):
     yield from run_attester_slashing_processing(spec, state, attester_slashing, False)
 
 
-@with_phases(['phase0'])
+@with_phases([PHASE0])
 @spec_state_test
 def test_unsorted_att_2(spec, state):
     attester_slashing = get_valid_attester_slashing(spec, state, signed_1=True, signed_2=False)
diff --git a/tests/core/pyspec/eth2spec/test/phase_1/block_processing/test_process_custody_key_reveal.py b/tests/core/pyspec/eth2spec/test/phase_1/block_processing/test_process_custody_key_reveal.py
index fb9157f2f..8c2436d5b 100644
--- a/tests/core/pyspec/eth2spec/test/phase_1/block_processing/test_process_custody_key_reveal.py
+++ b/tests/core/pyspec/eth2spec/test/phase_1/block_processing/test_process_custody_key_reveal.py
@@ -1,5 +1,6 @@
 from eth2spec.test.helpers.custody import get_valid_custody_key_reveal
 from eth2spec.test.context import (
+    PHASE0,
     with_all_phases_except,
     spec_state_test,
     expect_assertion_error,
@@ -54,7 +55,7 @@ def run_custody_key_reveal_processing(spec, state, custody_key_reveal, valid=Tru
     yield 'post', state
 
 
-@with_all_phases_except(['phase0'])
+@with_all_phases_except([PHASE0])
 @spec_state_test
 @always_bls
 def test_success(spec, state):
@@ -64,7 +65,7 @@ def test_success(spec, state):
     yield from run_custody_key_reveal_processing(spec, state, custody_key_reveal)
 
 
-@with_all_phases_except(['phase0'])
+@with_all_phases_except([PHASE0])
 @spec_state_test
 @always_bls
 def test_reveal_too_early(spec, state):
@@ -73,7 +74,7 @@ def test_reveal_too_early(spec, state):
     yield from run_custody_key_reveal_processing(spec, state, custody_key_reveal, False)
 
 
-@with_all_phases_except(['phase0'])
+@with_all_phases_except([PHASE0])
 @spec_state_test
 @always_bls
 def test_wrong_period(spec, state):
@@ -82,7 +83,7 @@ def test_wrong_period(spec, state):
     yield from run_custody_key_reveal_processing(spec, state, custody_key_reveal, False)
 
 
-@with_all_phases_except(['phase0'])
+@with_all_phases_except([PHASE0])
 @spec_state_test
 @always_bls
 def test_late_reveal(spec, state):
@@ -92,7 +93,7 @@ def test_late_reveal(spec, state):
     yield from run_custody_key_reveal_processing(spec, state, custody_key_reveal)
 
 
-@with_all_phases_except(['phase0'])
+@with_all_phases_except([PHASE0])
 @spec_state_test
 @always_bls
 def test_double_reveal(spec, state):
@@ -104,7 +105,7 @@ def test_double_reveal(spec, state):
     yield from run_custody_key_reveal_processing(spec, state, custody_key_reveal, False)
 
 
-@with_all_phases_except(['phase0'])
+@with_all_phases_except([PHASE0])
 @spec_state_test
 @always_bls
 def test_max_decrement(spec, state):
diff --git a/tests/core/pyspec/eth2spec/test/phase_1/block_processing/test_process_early_derived_secret_reveal.py b/tests/core/pyspec/eth2spec/test/phase_1/block_processing/test_process_early_derived_secret_reveal.py
index c5d9c5a63..83b0fe325 100644
--- a/tests/core/pyspec/eth2spec/test/phase_1/block_processing/test_process_early_derived_secret_reveal.py
+++ b/tests/core/pyspec/eth2spec/test/phase_1/block_processing/test_process_early_derived_secret_reveal.py
@@ -2,6 +2,7 @@ from eth2spec.test.helpers.custody import get_valid_early_derived_secret_reveal
 from eth2spec.test.helpers.block import apply_empty_block
 from eth2spec.test.helpers.state import next_epoch, get_balance
 from eth2spec.test.context import (
+    PHASE0,
     with_all_phases_except,
     spec_state_test,
     expect_assertion_error,
@@ -41,7 +42,7 @@ def run_early_derived_secret_reveal_processing(spec, state, randao_key_reveal, v
     yield 'post', state
 
 
-@with_all_phases_except(['phase0'])
+@with_all_phases_except([PHASE0])
 @spec_state_test
 @always_bls
 def test_success(spec, state):
@@ -50,7 +51,7 @@ def test_success(spec, state):
     yield from run_early_derived_secret_reveal_processing(spec, state, randao_key_reveal)
 
 
-@with_all_phases_except(['phase0'])
+@with_all_phases_except([PHASE0])
 @spec_state_test
 @never_bls
 def test_reveal_from_current_epoch(spec, state):
@@ -59,7 +60,7 @@ def test_reveal_from_current_epoch(spec, state):
     yield from run_early_derived_secret_reveal_processing(spec, state, randao_key_reveal, False)
 
 
-@with_all_phases_except(['phase0'])
+@with_all_phases_except([PHASE0])
 @spec_state_test
 @never_bls
 def test_reveal_from_past_epoch(spec, state):
@@ -70,7 +71,7 @@ def test_reveal_from_past_epoch(spec, state):
     yield from run_early_derived_secret_reveal_processing(spec, state, randao_key_reveal, False)
 
 
-@with_all_phases_except(['phase0'])
+@with_all_phases_except([PHASE0])
 @spec_state_test
 @always_bls
 def test_reveal_with_custody_padding(spec, state):
@@ -82,7 +83,7 @@ def test_reveal_with_custody_padding(spec, state):
     yield from run_early_derived_secret_reveal_processing(spec, state, randao_key_reveal, True)
 
 
-@with_all_phases_except(['phase0'])
+@with_all_phases_except([PHASE0])
 @spec_state_test
 @always_bls
 def test_reveal_with_custody_padding_minus_one(spec, state):
@@ -94,7 +95,7 @@ def test_reveal_with_custody_padding_minus_one(spec, state):
     yield from run_early_derived_secret_reveal_processing(spec, state, randao_key_reveal, True)
 
 
-@with_all_phases_except(['phase0'])
+@with_all_phases_except([PHASE0])
 @spec_state_test
 @never_bls
 def test_double_reveal(spec, state):
@@ -115,7 +116,7 @@ def test_double_reveal(spec, state):
     yield from run_early_derived_secret_reveal_processing(spec, state, randao_key_reveal2, False)
 
 
-@with_all_phases_except(['phase0'])
+@with_all_phases_except([PHASE0])
 @spec_state_test
 @never_bls
 def test_revealer_is_slashed(spec, state):
@@ -125,7 +126,7 @@ def test_revealer_is_slashed(spec, state):
     yield from run_early_derived_secret_reveal_processing(spec, state, randao_key_reveal, False)
 
 
-@with_all_phases_except(['phase0'])
+@with_all_phases_except([PHASE0])
 @spec_state_test
 @never_bls
 def test_far_future_epoch(spec, state):