diff --git a/test/Marketplace.test.js b/test/Marketplace.test.js
index 00b0ece..6dd11a8 100644
--- a/test/Marketplace.test.js
+++ b/test/Marketplace.test.js
@@ -41,6 +41,7 @@ const {
 } = require("./evm")
 const { getBytes } = require("ethers")
 const MarketplaceModule = require("../ignition/modules/marketplace")
+const { assertDeploymentRejectedWithCustomError } = require("./util")
 
 const ACCOUNT_STARTING_BALANCE = 1_000_000_000_000_000n
 
@@ -67,13 +68,7 @@ describe("Marketplace constructor", function () {
         },
       })
 
-      const error = await expect(promise).to.be.rejected
-      expect(error)
-        .to.have.property("message")
-        .that.contains(
-          expectedError,
-          `Expected error ${expectedError}, but got ${error.message}`
-        )
+      assertDeploymentRejectedWithCustomError(expectedError, promise)
     })
   }
 
@@ -101,13 +96,10 @@ describe("Marketplace constructor", function () {
       },
     })
 
-    const error = await expect(promise).to.be.rejected
-    expect(error)
-      .to.have.property("message")
-      .that.contains(
-        expectedError,
-        `Expected error ${expectedError}, but got ${error.message}`
-      )
+    assertDeploymentRejectedWithCustomError(
+      "Marketplace_MaximumSlashingTooHigh",
+      promise,
+    )
   })
 })
 
diff --git a/test/Periods.test.js b/test/Periods.test.js
index 49ac84d..1295140 100644
--- a/test/Periods.test.js
+++ b/test/Periods.test.js
@@ -1,5 +1,6 @@
 const { expect } = require("chai")
 const PeriodsModule = require("../ignition/modules/periods")
+const { assertDeploymentRejectedWithCustomError } = require("./util")
 
 describe("Periods", function () {
   it("should revert when secondsPerPeriod is 0", async function () {
@@ -10,15 +11,11 @@ describe("Periods", function () {
         },
       },
     })
-    const expectedError = "Periods_InvalidSecondsPerPeriod"
 
-    const error = await expect(promise).to.be.rejected
-    expect(error)
-      .to.have.property("message")
-      .that.contains(
-        expectedError,
-        `Expected error ${expectedError}, but got ${error.message}`,
-      )
+    assertDeploymentRejectedWithCustomError(
+      "Periods_InvalidSecondsPerPeriod",
+      promise,
+    )
   })
 
   it("should not revert when secondsPerPeriod more than 0", async function () {
diff --git a/test/util.js b/test/util.js
new file mode 100644
index 0000000..46bc91d
--- /dev/null
+++ b/test/util.js
@@ -0,0 +1,13 @@
+export async function assertDeploymentRejectedWithCustomError(
+  customError,
+  deploymentPromise,
+) {
+  const error = await expect(deploymentPromise).to.be.rejected
+
+  expect(error)
+    .to.have.property("message")
+    .that.contains(
+      customError,
+      `Expected error ${expectedError}, but got ${error.message}`,
+    )
+}