diff --git a/test/integration/contract.js b/test/integration/contract.js
index 65449b0d47..eb0b836c27 100644
--- a/test/integration/contract.js
+++ b/test/integration/contract.js
@@ -431,7 +431,7 @@ describe('Contract', function () {
       try {
         await contract.contractCompile(contractWithLib)
       } catch (e) {
-        e.message.indexOf('Couldn\'t find include file').should.not.be.equal(-1)
+        e.message.should.include('Couldn\'t find include file')
       }
     })
     it('Can deploy contract with external deps', async () => {
@@ -447,7 +447,7 @@ describe('Contract', function () {
       deployedStatic.result.should.have.property('returnType')
 
       const encodedCallData = await compiled.encodeCall('sumNumbers', ['1', '2'])
-      encodedCallData.indexOf('cb_').should.not.be.equal(-1)
+      encodedCallData.should.satisfy(s => s.startsWith('cb_'))
     })
     it('Can call contract with external deps', async () => {
       const callResult = await deployed.call('sumNumbers', ['1', '2'])
@@ -471,7 +471,7 @@ describe('Contract', function () {
         compiler.compilerVersion = '1.0.0'
         await compiler.checkCompatibility()
       } catch (e) {
-        e.message.indexOf('Unsupported compiler version 1.0.0').should.not.be.equal(-1)
+        e.message.should.satisfy(s => s.startsWith('Unsupported compiler version 1.0.0'))
       }
     })
     it('compile', async () => {
@@ -997,8 +997,7 @@ describe('Contract', function () {
           try {
             await contractObject.methods.hashFn(decoded)
           } catch (e) {
-            const isSizeCheck = e.message.indexOf('not a 32 bytes') !== -1
-            isSizeCheck.should.be.equal(true)
+            e.message.should.include('not a 32 bytes')
           }
         })
         it('Valid', async () => {
@@ -1024,8 +1023,7 @@ describe('Contract', function () {
           try {
             await contractObject.methods.signatureFn(decoded)
           } catch (e) {
-            const isSizeCheck = e.message.indexOf('not a 64 bytes') !== -1
-            isSizeCheck.should.be.equal(true)
+            e.message.should.include('not a 64 bytes')
           }
         })
         it('Valid', async () => {
@@ -1052,8 +1050,7 @@ describe('Contract', function () {
           try {
             await contractObject.methods.bytesFn(Buffer.from([...decoded, 2]))
           } catch (e) {
-            const isSizeCheck = e.message.indexOf('not a 32 bytes') !== -1
-            isSizeCheck.should.be.equal(true)
+            e.message.should.include('not a 32 bytes')
           }
         })
         it('Valid', async () => {