diff --git a/testing/_test_suite.ts b/testing/_test_suite.ts
index 9a0696a6f..805a8b093 100644
--- a/testing/_test_suite.ts
+++ b/testing/_test_suite.ts
@@ -84,7 +84,9 @@ export class TestSuiteInternal<T> implements TestSuite<T> {
 
     const { suite } = describe;
     if (suite && !TestSuiteInternal.suites.has(suite.symbol)) {
-      throw new Error("suite does not represent a registered test suite");
+      throw new Error(
+        "Cannot construct Test Suite: suite does not represent a registered test suite",
+      );
     }
     const testSuite = suite
       ? TestSuiteInternal.suites.get(suite.symbol)
@@ -101,7 +103,7 @@ export class TestSuiteInternal<T> implements TestSuite<T> {
         const value = fn() as any;
         if (value instanceof Promise) {
           throw new Error(
-            'Returning a Promise from "describe" is not supported. Tests must be defined synchronously.',
+            'Returning a Promise from "describe" is not supported: tests must be defined synchronously',
           );
         }
       } finally {
diff --git a/testing/bdd.ts b/testing/bdd.ts
index 8b1a884cc..81a8e7f71 100644
--- a/testing/bdd.ts
+++ b/testing/bdd.ts
@@ -562,7 +562,7 @@ export interface it {
 export function it<T>(...args: ItArgs<T>) {
   if (TestSuiteInternal.runningCount > 0) {
     throw new Error(
-      "cannot register new test cases after already registered test cases start running",
+      "Cannot register new test cases after already registered test cases start running",
     );
   }
   const options = itDefinition(...args);
@@ -717,7 +717,7 @@ function addHook<T>(
   if (!TestSuiteInternal.current) {
     if (TestSuiteInternal.started) {
       throw new Error(
-        "cannot add global hooks after a global test is registered",
+        "Cannot add global hooks after a global test is registered",
       );
     }
     TestSuiteInternal.current = new TestSuiteInternal({
@@ -1070,7 +1070,7 @@ export function describe<T>(
 ): TestSuite<T> {
   if (TestSuiteInternal.runningCount > 0) {
     throw new Error(
-      "cannot register new test suites after already registered test cases start running",
+      "Cannot register new test suites after already registered test cases start running",
     );
   }
   const options = describeDefinition(...args);
diff --git a/testing/bdd_test.ts b/testing/bdd_test.ts
index dd133dc30..2ab8c4725 100644
--- a/testing/bdd_test.ts
+++ b/testing/bdd_test.ts
@@ -2055,7 +2055,7 @@ Deno.test("describe()", async (t) => {
         // deno-lint-ignore no-explicit-any
         () => describe("async describe", (async () => {}) as any),
         Error,
-        'Returning a Promise from "describe" is not supported. Tests must be defined synchronously.',
+        'Returning a Promise from "describe" is not supported: tests must be defined synchronously',
       );
     },
   );
diff --git a/testing/mock.ts b/testing/mock.ts
index 8cc1ce533..b542f218e 100644
--- a/testing/mock.ts
+++ b/testing/mock.ts
@@ -435,7 +435,9 @@ function functionSpy<
     restore: {
       enumerable: true,
       value: () => {
-        throw new MockError("Function cannot be restored");
+        throw new MockError(
+          "Cannot restore: function cannot be restored",
+        );
       },
     },
   });
@@ -643,15 +645,21 @@ function methodSpy<
   Return,
 >(self: Self, property: keyof Self): MethodSpy<Self, Args, Return> {
   if (typeof self[property] !== "function") {
-    throw new MockError("Property is not an instance method");
+    throw new MockError(
+      "Cannot spy: property is not an instance method",
+    );
   }
   if (isSpy(self[property])) {
-    throw new MockError("Already spying on instance method");
+    throw new MockError(
+      "Cannot spy: already spying on instance method",
+    );
   }
 
   const propertyDescriptor = Object.getOwnPropertyDescriptor(self, property);
   if (propertyDescriptor && !propertyDescriptor.configurable) {
-    throw new MockError("Cannot spy on non-configurable instance method");
+    throw new MockError(
+      "Cannot spy: non-configurable instance method",
+    );
   }
 
   const original = self[property] as unknown as (
@@ -690,7 +698,9 @@ function methodSpy<
       enumerable: true,
       value: () => {
         if (restored) {
-          throw new MockError("Instance method already restored");
+          throw new MockError(
+            "Cannot restore: instance method already restored",
+          );
         }
         if (propertyDescriptor) {
           Object.defineProperty(self, property, propertyDescriptor);
@@ -767,7 +777,9 @@ function constructorSpy<
     static readonly calls = calls;
     static readonly restored = false;
     static restore() {
-      throw new MockError("Constructor cannot be restored");
+      throw new MockError(
+        "Cannot restore: constructor cannot be restored",
+      );
     }
   } as ConstructorSpy<Self, Args>;
   return spy;
@@ -1082,15 +1094,19 @@ export function stub<
   func?: (this: Self, ...args: Args) => Return,
 ): Stub<Self, Args, Return> {
   if (self[property] !== undefined && typeof self[property] !== "function") {
-    throw new MockError("Property is not an instance method");
+    throw new MockError(
+      "Cannot stub: property is not an instance method",
+    );
   }
   if (isSpy(self[property])) {
-    throw new MockError("Already spying on instance method");
+    throw new MockError(
+      "Cannot stub: already spying on instance method",
+    );
   }
 
   const propertyDescriptor = Object.getOwnPropertyDescriptor(self, property);
   if (propertyDescriptor && !propertyDescriptor.configurable) {
-    throw new MockError("Cannot stub non-configurable instance method");
+    throw new MockError("Cannot stub: non-configurable instance method");
   }
 
   const fake = func ?? (() => {}) as (this: Self, ...args: Args) => Return;
@@ -1135,7 +1151,9 @@ export function stub<
       enumerable: true,
       value: () => {
         if (restored) {
-          throw new MockError("Instance method already restored");
+          throw new MockError(
+            "Cannot restore: instance method already restored",
+          );
         }
         if (propertyDescriptor) {
           Object.defineProperty(self, property, propertyDescriptor);
diff --git a/testing/mock_test.ts b/testing/mock_test.ts
index de83b38e1..51326b2cd 100644
--- a/testing/mock_test.ts
+++ b/testing/mock_test.ts
@@ -79,7 +79,7 @@ Deno.test("spy()", () => {
   assertThrows(
     () => func.restore(),
     MockError,
-    "Function cannot be restore",
+    "Cannot restore: function cannot be restored",
   );
   assertEquals(func.restored, false);
 });
@@ -125,7 +125,7 @@ Deno.test("spy() works on function", () => {
   assertThrows(
     () => func.restore(),
     MockError,
-    "Function cannot be restored",
+    "Cannot restore: function cannot be restored",
   );
   assertEquals(func.restored, false);
 
@@ -239,7 +239,7 @@ Deno.test("spy() works on instance method", () => {
   assertThrows(
     () => func.restore(),
     MockError,
-    "Instance method already restored",
+    "Cannot restore: instance method already restored",
   );
   assertEquals(func.restored, true);
 });
@@ -277,7 +277,7 @@ Deno.test("spy() works on instance method symbol", () => {
   assertThrows(
     () => func.restore(),
     MockError,
-    "Instance method already restored",
+    "Cannot restore: instance method already restored",
   );
   assertEquals(func.restored, true);
 });
@@ -342,7 +342,7 @@ Deno.test("spy() works on instance method property descriptor", () => {
   assertThrows(
     () => action.restore(),
     MockError,
-    "Instance method already restored",
+    "Cannot restore: instance method already restored",
   );
   assertEquals(action.restored, true);
 });
@@ -444,7 +444,7 @@ Deno.test("spy() supports explicit resource management", () => {
         if (funcRef) funcRef.restore();
       },
       MockError,
-      "Instance method already restored",
+      "Cannot restore: instance method already restored",
     );
     assertEquals(funcRef.restored, true);
   }
@@ -478,7 +478,7 @@ Deno.test("spy() works on constructor", () => {
   assertThrows(
     () => PointSpy.restore(),
     MockError,
-    "Constructor cannot be restored",
+    "Cannot restore: constructor cannot be restored",
   );
 });
 
@@ -546,7 +546,7 @@ Deno.test("spy() throws when try spying already spied method", () => {
   assertThrows(
     () => spy(obj, "fn"),
     MockError,
-    "Already spying on instance method",
+    "Cannot spy: already spying on instance method",
   );
 });
 
@@ -556,7 +556,7 @@ Deno.test("spy() throws when the property is not a method", () => {
     // deno-lint-ignore no-explicit-any
     () => spy(obj as any, "fn"),
     MockError,
-    "Property is not an instance method",
+    "Cannot spy: property is not an instance method",
   );
 });
 
@@ -566,7 +566,7 @@ Deno.test("spy() throws when the property is not configurable", () => {
   assertThrows(
     () => spy(obj, "fn"),
     MockError,
-    "Cannot spy on non-configurable instance method",
+    "Cannot spy: non-configurable instance method",
   );
 });
 
@@ -602,7 +602,7 @@ Deno.test("stub()", () => {
   assertThrows(
     () => func.restore(),
     MockError,
-    "Instance method already restored",
+    "Cannot restore: instance method already restored",
   );
   assertEquals(func.restored, true);
 });
@@ -640,7 +640,7 @@ Deno.test("stub() works on function", () => {
   assertThrows(
     () => func.restore(),
     MockError,
-    "Instance method already restored",
+    "Cannot restore: instance method already restored",
   );
   assertEquals(func.restored, true);
 });
@@ -684,7 +684,7 @@ Deno.test("stub() supports explicit resource management", () => {
         if (funcRef) funcRef.restore();
       },
       MockError,
-      "Instance method already restored",
+      "Cannot restore: instance method already restored",
     );
     assertEquals(funcRef.restored, true);
   }
@@ -727,7 +727,7 @@ Deno.test("stub() handles non existent function", () => {
   assertThrows(
     () => func.restore(),
     MockError,
-    "Instance method already restored",
+    "Cannot restore: instance method already restored",
   );
   assertEquals(func.restored, true);
 });
@@ -797,7 +797,7 @@ Deno.test("stub() throws when the property is not a method", () => {
     // deno-lint-ignore no-explicit-any
     () => stub(obj as any, "fn"),
     MockError,
-    "Property is not an instance method",
+    "Cannot stub: property is not an instance method",
   );
 });
 
@@ -807,7 +807,7 @@ Deno.test("stub() throws when try stubbing already stubbed method", () => {
   assertThrows(
     () => stub(obj, "fn"),
     MockError,
-    "Already spying on instance method",
+    "Cannot stub: already spying on instance method",
   );
 });
 
@@ -817,7 +817,7 @@ Deno.test("stub() throws then the property is not configurable", () => {
   assertThrows(
     () => stub(obj, "fn"),
     MockError,
-    "Cannot stub non-configurable instance method",
+    "Cannot stub: non-configurable instance method",
   );
 });
 
diff --git a/testing/time.ts b/testing/time.ts
index 150b7182c..59ba6a44c 100644
--- a/testing/time.ts
+++ b/testing/time.ts
@@ -134,12 +134,12 @@ function fakeSetTimeout(
   // deno-lint-ignore no-explicit-any
   ...args: any[]
 ): number {
-  if (!time) throw new TimeError("Time is not faked");
+  if (!time) throw new TimeError("Cannot set timeout: time is not faked");
   return setTimer(callback, delay, args, false);
 }
 
 function fakeClearTimeout(id?: unknown) {
-  if (!time) throw new TimeError("Time is not faked");
+  if (!time) throw new TimeError("Cannot clear timeout: time is not faked");
   if (typeof id === "number" && dueNodes.has(id)) {
     dueNodes.delete(id);
   }
@@ -152,12 +152,12 @@ function fakeSetInterval(
   // deno-lint-ignore no-explicit-any
   ...args: any[]
 ): number {
-  if (!time) throw new TimeError("Time is not faked");
+  if (!time) throw new TimeError("Cannot set interval: time is not faked");
   return setTimer(callback, delay, args, true);
 }
 
 function fakeClearInterval(id?: unknown) {
-  if (!time) throw new TimeError("Time is not faked");
+  if (!time) throw new TimeError("Cannot clear interval: time is not faked");
   if (typeof id === "number" && dueNodes.has(id)) {
     dueNodes.delete(id);
   }
@@ -294,7 +294,9 @@ export class FakeTime {
     start?: number | string | Date | null,
     options?: FakeTimeOptions,
   ) {
-    if (time) throw new TimeError("Time is already faked");
+    if (time) {
+      throw new TimeError("Cannot construct FakeTime: time is already faked");
+    }
     initializedAt = _internals.Date.now();
     startedAt = start instanceof Date
       ? start.valueOf()
@@ -303,7 +305,11 @@ export class FakeTime {
       : typeof start === "string"
       ? (new Date(start)).valueOf()
       : initializedAt;
-    if (Number.isNaN(startedAt)) throw new TypeError("Invalid start time");
+    if (Number.isNaN(startedAt)) {
+      throw new TypeError(
+        `Cannot construct FakeTime: invalid start time ${startedAt}`,
+      );
+    }
     now = startedAt;
 
     timerId = timerIdGen();
@@ -381,7 +387,9 @@ export class FakeTime {
    * ```
    */
   static restore() {
-    if (!time) throw new TimeError("Time is already restored");
+    if (!time) {
+      throw new TimeError("Cannot restore time: time is already restored");
+    }
     time.restore();
   }
 
@@ -417,7 +425,11 @@ export class FakeTime {
     // deno-lint-ignore no-explicit-any
     ...args: any[]
   ): Promise<T> {
-    if (!time) return Promise.reject(new TimeError("Time is not faked"));
+    if (!time) {
+      return Promise.reject(
+        new TimeError("Cannot restore time: time is not faked"),
+      );
+    }
     restoreGlobals();
     try {
       const result = callback.apply(null, args);
@@ -478,7 +490,11 @@ export class FakeTime {
    * @param value The current time (in milliseconds)
    */
   set now(value: number) {
-    if (value < now) throw new RangeError("Time cannot go backwards");
+    if (value < now) {
+      throw new RangeError(
+        `Cannot set current time in the past, time must be >= ${now}: received ${value}`,
+      );
+    }
     let dueNode: DueNode | null = dueTree.min();
     while (dueNode && dueNode.due <= value) {
       const timer: Timer | undefined = dueNode.timers.shift();
@@ -803,7 +819,9 @@ export class FakeTime {
    * ```
    */
   restore() {
-    if (!time) throw new TimeError("Time is already restored");
+    if (!time) {
+      throw new TimeError("Cannot restore time: time is already restored");
+    }
     time = undefined;
     restoreGlobals();
     if (advanceIntervalId) clearInterval(advanceIntervalId);
diff --git a/testing/time_test.ts b/testing/time_test.ts
index 632b1f6fe..33b8c5973 100644
--- a/testing/time_test.ts
+++ b/testing/time_test.ts
@@ -339,7 +339,7 @@ Deno.test("FakeTime.restoreFor() returns promise that rejected to TimeError if F
   await assertRejects(
     () => FakeTime.restoreFor(() => {}),
     TimeError,
-    "Time is not faked",
+    "Cannot restore time: time is not faked",
   );
 });
 
@@ -662,15 +662,23 @@ Deno.test("Faked timer functions throws when called after FakeTime is restored",
   assertThrows(
     () => fakeSetTimeout(() => {}, 0),
     TimeError,
-    "Time is not faked",
+    "Cannot set timeout: time is not faked",
+  );
+  assertThrows(
+    () => fakeClearTimeout(0),
+    TimeError,
+    "Cannot clear timeout: time is not faked",
   );
-  assertThrows(() => fakeClearTimeout(0), TimeError, "Time is not faked");
   assertThrows(
     () => fakeSetInterval(() => {}, 0),
     TimeError,
-    "Time is not faked",
+    "Cannot set interval: time is not faked",
+  );
+  assertThrows(
+    () => fakeClearInterval(0),
+    TimeError,
+    "Cannot clear interval: time is not faked",
   );
-  assertThrows(() => fakeClearInterval(0), TimeError, "Time is not faked");
 });
 
 Deno.test("Faked Date.now returns real time after FakeTime is restored", () => {
@@ -700,19 +708,31 @@ Deno.test("FakeTime can be constructed with number, Date, or string", () => {
 });
 
 Deno.test("FakeTime throws when NaN is provided", () => {
-  assertThrows(() => new FakeTime(NaN), TypeError, "Invalid start time");
+  assertThrows(
+    () => new FakeTime(NaN),
+    TypeError,
+    "Cannot construct FakeTime: invalid start time NaN",
+  );
 });
 
 Deno.test("FakeTime.restore() throws when the time is already restored", () => {
   const _time = new FakeTime();
   FakeTime.restore();
-  assertThrows(() => FakeTime.restore(), TimeError, "Time is already restored");
+  assertThrows(
+    () => FakeTime.restore(),
+    TimeError,
+    "Cannot restore time: time is already restored",
+  );
 });
 
 Deno.test("time.restore() throws when the time is already restored", () => {
   const time = new FakeTime();
   time.restore();
-  assertThrows(() => time.restore(), TimeError, "Time is already restored");
+  assertThrows(
+    () => time.restore(),
+    TimeError,
+    "Cannot restore time: time is already restored",
+  );
 });
 
 Deno.test("time.now = N throws when N < time.now", () => {
@@ -722,7 +742,7 @@ Deno.test("time.now = N throws when N < time.now", () => {
       time.now = 999;
     },
     RangeError,
-    "Time cannot go backwards",
+    "Cannot set current time in the past, time must be >= 1000: received 999",
   );
 });