diff --git a/packages/cashscript/test/Contract.test.ts b/packages/cashscript/test/Contract.test.ts
index 14e595b6..a31a16d0 100644
--- a/packages/cashscript/test/Contract.test.ts
+++ b/packages/cashscript/test/Contract.test.ts
@@ -11,21 +11,24 @@ import {
 import {
   alicePkh, alicePriv, alicePub, bobPriv,
 } from './fixture/vars.js';
-import p2pkhArtifact from './fixture/p2pkh.json' with { type: 'json' };
-import twtArtifact from './fixture/transfer_with_timeout.json' with { type: 'json' };
-import hodlVaultArtifact from './fixture/hodl_vault.json' with { type: 'json' };
-import mecenasArtifact from './fixture/mecenas.json' with { type: 'json' };
+import p2pkhArtifact from './fixture/p2pkh.artifact.js';
+import twtArtifact from './fixture/transfer_with_timeout.artifact.js';
+import hodlVaultArtifact from './fixture/hodl_vault.artifact.js';
+import mecenasArtifact from './fixture/mecenas.artifact.js';
 import deprecatedMecenasArtifact from './fixture/deprecated/mecenas-v0.6.0.json' with { type: 'json' };
-import boundedBytesArtifact from './fixture/bounded_bytes.json' with { type: 'json' };
+import boundedBytesArtifact from './fixture/bounded_bytes.artifact.js';
 
 describe('Contract', () => {
   describe('new', () => {
     it('should fail with incorrect constructor args', () => {
       const provider = new ElectrumNetworkProvider(Network.CHIPNET);
 
+      // @ts-expect-error invalid constructor type
       expect(() => new Contract(p2pkhArtifact, [], { provider })).toThrow();
+      // @ts-expect-error invalid constructor type
       expect(() => new Contract(p2pkhArtifact, [20n], { provider })).toThrow();
       expect(
+        // @ts-expect-error invalid constructor type
         () => new Contract(p2pkhArtifact, [placeholder(20), placeholder(20)], { provider }),
       ).toThrow();
       expect(() => new Contract(p2pkhArtifact, [placeholder(19)], { provider })).toThrow();
@@ -62,8 +65,7 @@ describe('Contract', () => {
 
     it('should create new TransferWithTimeout instance', () => {
       const provider = new ElectrumNetworkProvider(Network.CHIPNET);
-      const constructorArgs = [placeholder(65), placeholder(65), 1000000n];
-      const instance = new Contract(twtArtifact, constructorArgs, { provider });
+      const instance = new Contract(twtArtifact, [placeholder(65), placeholder(65), 1000000n], { provider });
 
       expect(typeof instance.address).toBe('string');
       expect(typeof instance.functions.transfer).toBe('function');
@@ -73,8 +75,7 @@ describe('Contract', () => {
 
     it('should create new HodlVault instance', () => {
       const provider = new ElectrumNetworkProvider(Network.CHIPNET);
-      const constructorArgs = [placeholder(65), placeholder(65), 1000000n, 10000n];
-      const instance = new Contract(hodlVaultArtifact, constructorArgs, { provider });
+      const instance = new Contract(hodlVaultArtifact, [placeholder(65), placeholder(65), 1000000n, 10000n], { provider });
 
       expect(typeof instance.address).toBe('string');
       expect(typeof instance.functions.spend).toBe('function');
@@ -83,8 +84,7 @@ describe('Contract', () => {
 
     it('should create new Mecenas instance', () => {
       const provider = new ElectrumNetworkProvider(Network.CHIPNET);
-      const constructorArgs = [placeholder(20), placeholder(20), 1000000n];
-      const instance = new Contract(mecenasArtifact, constructorArgs, { provider });
+      const instance = new Contract(mecenasArtifact, [placeholder(20), placeholder(20), 1000000n], { provider });
 
       expect(typeof instance.address).toBe('string');
       expect(typeof instance.functions.receive).toBe('function');
diff --git a/packages/cashscript/test/TransactionBuilder.test.ts b/packages/cashscript/test/TransactionBuilder.test.ts
index 59e94028..8e8738a4 100644
--- a/packages/cashscript/test/TransactionBuilder.test.ts
+++ b/packages/cashscript/test/TransactionBuilder.test.ts
@@ -12,8 +12,8 @@ import {
 } from './fixture/vars.js';
 import { Network } from '../src/interfaces.js';
 import { utxoComparator, calculateDust, randomUtxo, randomToken, isNonTokenUtxo, isFungibleTokenUtxo } from '../src/utils.js';
-import p2pkhArtifact from './fixture/p2pkh.json' with { type: 'json' };
-import twtArtifact from './fixture/transfer_with_timeout.json' with { type: 'json' };
+import p2pkhArtifact from './fixture/p2pkh.artifact.js';
+import twtArtifact from './fixture/transfer_with_timeout.artifact.js';
 import { TransactionBuilder } from '../src/TransactionBuilder.js';
 import { gatherUtxos, getTxOutputs } from './test-util.js';
 
@@ -22,8 +22,8 @@ describe('Transaction Builder', () => {
     ? new MockNetworkProvider()
     : new ElectrumNetworkProvider(Network.CHIPNET);
 
-  let p2pkhInstance: Contract;
-  let twtInstance: Contract;
+  let p2pkhInstance: Contract<typeof p2pkhArtifact>;
+  let twtInstance: Contract<typeof twtArtifact>;
 
   beforeAll(() => {
     // Note: We instantiate the contract with carolPkh to avoid mempool conflicts with other (P2PKH) tests
diff --git a/packages/cashscript/test/e2e/P2PKH-tokens.test.ts b/packages/cashscript/test/e2e/P2PKH-tokens.test.ts
index dbca1fcb..933a41dd 100644
--- a/packages/cashscript/test/e2e/P2PKH-tokens.test.ts
+++ b/packages/cashscript/test/e2e/P2PKH-tokens.test.ts
@@ -9,10 +9,10 @@ import {
 } from '../fixture/vars.js';
 import { getTxOutputs } from '../test-util.js';
 import { Network, TokenDetails, Utxo } from '../../src/interfaces.js';
-import artifact from '../fixture/p2pkh.json' with { type: 'json' };
+import artifact from '../fixture/p2pkh.artifact.js';
 
 describe('P2PKH-tokens', () => {
-  let p2pkhInstance: Contract;
+  let p2pkhInstance: Contract<typeof artifact>;
 
   beforeAll(() => {
     const provider = process.env.TESTS_USE_MOCKNET
diff --git a/packages/cashscript/test/e2e/TokenCategoryCheck.test.ts b/packages/cashscript/test/e2e/TokenCategoryCheck.test.ts
index 36ca67ba..ab95ba9a 100644
--- a/packages/cashscript/test/e2e/TokenCategoryCheck.test.ts
+++ b/packages/cashscript/test/e2e/TokenCategoryCheck.test.ts
@@ -4,7 +4,7 @@ import {
   TransactionBuilder,
 } from '../../src/index.js';
 import { Network } from '../../src/interfaces.js';
-import artifact from '../fixture/token_category_comparison.json' with { type: 'json' };
+import artifact from '../fixture/token_category_comparison.artifact.js';
 
 describe('TokenCategoryCheck', () => {
   const provider = process.env.TESTS_USE_MOCKNET
diff --git a/packages/cashscript/test/e2e/misc/timelocks.test.ts b/packages/cashscript/test/e2e/misc/timelocks.test.ts
index bb329e96..03ed406b 100644
--- a/packages/cashscript/test/e2e/misc/timelocks.test.ts
+++ b/packages/cashscript/test/e2e/misc/timelocks.test.ts
@@ -9,8 +9,8 @@ import {
 } from '../../fixture/vars.js';
 import { Network } from '../../../src/interfaces.js';
 import { utxoComparator, calculateDust, randomUtxo, isNonTokenUtxo } from '../../../src/utils.js';
-import p2pkhArtifact from '../../fixture/p2pkh.json' with { type: 'json' };
-import twtArtifact from '../../fixture/transfer_with_timeout.json' with { type: 'json' };
+import p2pkhArtifact from '../../fixture/p2pkh.artifact.js';
+import twtArtifact from '../../fixture/transfer_with_timeout.artifact.js';
 import { TransactionBuilder } from '../../../src/TransactionBuilder.js';
 import { describeOrSkip, getTxOutputs } from '../../test-util.js';
 
@@ -20,8 +20,8 @@ describe('Timelocks', () => {
     ? new MockNetworkProvider()
     : new ElectrumNetworkProvider(Network.CHIPNET);
 
-  let p2pkhInstance: Contract;
-  let twtInstance: Contract;
+  let p2pkhInstance: Contract<typeof p2pkhArtifact>;
+  let twtInstance: Contract<typeof twtArtifact>;
 
   beforeAll(() => {
     // Note: We instantiate the contract with carolPkh to avoid mempool conflicts with other (P2PKH) tests
diff --git a/packages/cashscript/test/e2e/network/FullStack.test.ts b/packages/cashscript/test/e2e/network/FullStack.test.ts
index 4fb3fd7e..7f2472f0 100644
--- a/packages/cashscript/test/e2e/network/FullStack.test.ts
+++ b/packages/cashscript/test/e2e/network/FullStack.test.ts
@@ -8,7 +8,7 @@ import {
 } from '../../fixture/vars.js';
 import { describeOrSkip, getTxOutputs } from '../../test-util.js';
 import { FailedRequireError } from '../../../src/Errors.js';
-import artifact from '../../fixture/p2pkh.json' with { type: 'json' };
+import artifact from '../../fixture/p2pkh.artifact.js';
 
 describeOrSkip(!process.env.TESTS_USE_MOCKNET, 'test FullStackNetworkProvider', () => {
   const provider = new FullStackNetworkProvider('mainnet', new BCHJS({ restURL: 'https://api.fullstack.cash/v5/' }));