diff --git a/.unimportedrc.json b/.unimportedrc.json
index 568b965b8..5f7633de4 100644
--- a/.unimportedrc.json
+++ b/.unimportedrc.json
@@ -1,8 +1,23 @@
 {
-  "entry": ["lib/sinon.js", "lib/sinon-esm.js"],
-  "extensions": [".js"],
-  "ignorePatterns": ["**/node_modules/**"],
+  "entry": [
+    "lib/sinon.js",
+    "lib/sinon-esm.js",
+    "test/**/*-test.js",
+    "test/webworker/webworker-script.js",
+    "test/webworker/webworker-support-assessment.js"
+  ],
+  "extensions": [
+    ".js"
+  ],
+  "ignorePatterns": [
+    "**/node_modules/**"
+  ],
   "ignoreUnresolved": [],
-  "ignoreUnimported": ["docs/**", "pkg/**", "test/**"],
+  "ignoreUnimported": [
+    "docs/**",
+    "pkg/**",
+    "vendor/**/*",
+    "test/es2015/check-esm-bundle-is-runnable.js"
+  ],
   "ignoreUnused": []
 }
diff --git a/lib/create-sinon-api.js b/lib/create-sinon-api.js
index 8e9d1ca49..9ef9ec126 100644
--- a/lib/create-sinon-api.js
+++ b/lib/create-sinon-api.js
@@ -21,7 +21,6 @@ module.exports = function createApi(opts = { sinonXhrLib: nise }) {
 
     const apiMethods = {
         createSandbox: createSandbox,
-        assert: require("./sinon/assert"),
         match: require("@sinonjs/samsam").createMatcher,
         restoreObject: require("./sinon/restore-object"),
 
diff --git a/lib/sinon/assert.js b/lib/sinon/assert.js
index fc7dbdbe3..43a555804 100644
--- a/lib/sinon/assert.js
+++ b/lib/sinon/assert.js
@@ -1,4 +1,5 @@
 "use strict";
+/** @module */
 
 const arrayProto = require("@sinonjs/commons").prototypes.array;
 const calledInOrder = require("@sinonjs/commons").calledInOrder;
@@ -15,12 +16,48 @@ const forEach = arrayProto.forEach;
 const join = arrayProto.join;
 const splice = arrayProto.splice;
 
-function createAssertObject() {
+function applyDefaults(obj, defaults) {
+    for (const key of Object.keys(defaults)) {
+        const val = obj[key];
+        if (val === null || typeof val === "undefined") {
+            obj[key] = defaults[key];
+        }
+    }
+}
+
+/**
+ * @typedef {object} CreateAssertOptions
+ * @global
+ *
+ * @property {boolean} [shouldLimitAssertionLogs] default is false
+ * @property {number}  [assertionLogLimit] default is 10K
+ */
+
+/**
+ * Create an assertion object that exposes several methods to invoke
+ *
+ * @param {CreateAssertOptions}  [opts] options bag
+ * @returns {object} object with multiple assertion methods
+ */
+function createAssertObject(opts) {
+    const cleanedAssertOptions = opts || {};
+    applyDefaults(cleanedAssertOptions, {
+        shouldLimitAssertionLogs: false,
+        assertionLogLimit: 1e4,
+    });
+
     const assert = {
         failException: "AssertError",
 
         fail: function fail(message) {
-            const error = new Error(message);
+            let msg = message;
+            if (cleanedAssertOptions.shouldLimitAssertionLogs) {
+                msg = message.substring(
+                    0,
+                    cleanedAssertOptions.assertionLogLimit,
+                );
+            }
+            const error = new Error(msg);
             error.name = this.failException || assert.failException;
 
             throw error;
diff --git a/lib/sinon/create-sandbox.js b/lib/sinon/create-sandbox.js
index b958daf0c..2d29cf29c 100644
--- a/lib/sinon/create-sandbox.js
+++ b/lib/sinon/create-sandbox.js
@@ -7,7 +7,7 @@ const forEach = arrayProto.forEach;
 const push = arrayProto.push;
 
 function prepareSandboxFromConfig(config) {
-    const sandbox = new Sandbox();
+    const sandbox = new Sandbox({ assertOptions: config.assertOptions });
 
     if (config.useFakeServer) {
         if (typeof config.useFakeServer === "object") {
@@ -41,6 +41,34 @@ function exposeValue(sandbox, config, key, value) {
     }
 }
 
+/**
+ * Customize the sandbox.
+ * This is mostly an integration feature most users will not need
+ *
+ * @typedef {object} SandboxConfig
+ * @property {string[]} properties The properties of the API to expose on the sandbox. Examples: ['spy', 'fake', 'restore']
+ * @property {(object|null)} injectInto TBD
+ * @property {boolean} useFakeTimers  whether timers are faked by default
+ * @property {boolean} useFakeServer  whether XHR's are faked and the server feature enabled by default
+ * @property {object} [assertOptions] see CreateAssertOptions in ./assert
+ */
+// This type def is really suffering from JSDoc not being
+// able to reference types in other modules
+
+/**
+ * A configured sinon sandbox.
+ *
+ * @typedef {object} ConfiguredSinonSandboxType
+ * @augments Sandbox
+ * @property {string[]} injectedKeys the keys that have been injected (from config.injectInto)
+ * @property {*} injectInto TBD
+ * @property {*[]} args the arguments for the sandbox
+ */
+
+/**
+ * @param config {SandboxConfig}
+ * @returns {Sandbox}
+ */
 function createSandbox(config) {
     if (!config) {
         return new Sandbox();
diff --git a/lib/sinon/sandbox.js b/lib/sinon/sandbox.js
index ce25a2240..6bab45f96 100644
--- a/lib/sinon/sandbox.js
+++ b/lib/sinon/sandbox.js
@@ -69,8 +69,16 @@ function checkForValidArguments(descriptor, property, replacement) {
     }
 }
 
-function Sandbox() {
+/**
+ * A sinon sandbox
+ *
+ * @param opts
+ * @param {object} [opts.assertOptions] see the CreateAssertOptions in ./assert
+ * @class
+ */
+function Sandbox(opts = {}) {
     const sandbox = this;
+    const assertOptions = opts.assertOptions || {};
     let fakeRestorers = [];
     let promiseLib;
 
@@ -91,7 +99,7 @@ function Sandbox() {
         }
     }
 
-    sandbox.assert = sinonAssert.createAssertObject();
+    sandbox.assert = sinonAssert.createAssertObject(assertOptions);
 
     sandbox.serverPrototype = fakeServer;
 
diff --git a/test/assert-test.js b/test/assert-test.js
index 036dc2231..69b675017 100644
--- a/test/assert-test.js
+++ b/test/assert-test.js
@@ -65,6 +65,18 @@ describe("assert", function () {
             sinonAssert.failException = this.exceptionName;
         });
 
+        it("can be configured to limit the error message length", function () {
+            const customAssert = sinonAssert.createAssertObject({
+                shouldLimitAssertionLogs: true,
+                assertionLogLimit: 10,
+            });
+
+            assert.exception(
+                () => customAssert.fail("1234567890--THIS SHOULD NOT SHOW--"),
+                { message: "1234567890" },
+            );
+        });
+
         it("throws exception", function () {
             assert.exception(
                 function () {
diff --git a/test/create-sandbox-test.js b/test/create-sandbox-test.js
new file mode 100644
index 000000000..66656c13b
--- /dev/null
+++ b/test/create-sandbox-test.js
@@ -0,0 +1,22 @@
+"use strict";
+
+const createSandbox = require("../lib/sinon/create-sandbox");
+const { assert } = require("@sinonjs/referee");
+
+describe("create-sandbox", function () {
+    it("can be configured to limit the error message length", function () {
+        // Arrange & Act
+        const sb = createSandbox({
+            assertOptions: {
+                shouldLimitAssertionLogs: true,
+                assertionLogLimit: 10,
+            },
+        });
+
+        // Assert
+        assert.exception(
+            () => sb.assert.fail("1234567890--THIS SHOULD NOT SHOW--"),
+            { message: "1234567890" },
+        );
+    });
+});