4 files changed, 11 insertions, 17 deletions
diff --git a/testing/asserts.ts b/testing/asserts.ts
index a2583c22a..cbdaf3a94 100644
--- a/testing/asserts.ts
+++ b/testing/asserts.ts
@@ -183,7 +183,7 @@ export function assertArrayContains(
   expected: unknown[],
   msg?: string
 ): void {
-  let missing = [];
+  let missing: unknown[] = [];
   for (let i = 0; i < expected.length; i++) {
     let found = false;
     for (let j = 0; j < actual.length; j++) {
diff --git a/testing/format.ts b/testing/format.ts
index 8ed066eb0..af8391b23 100644
--- a/testing/format.ts
+++ b/testing/format.ts
@@ -525,16 +525,10 @@ const getConfig = (options: Options): Config => ({
  */
 // eslint-disable-next-line @typescript-eslint/no-explicit-any
 export function format(val: any, options: Optional<Options> = {}): string {
-  const opts = Object.keys(DEFAULT_OPTIONS).reduce(
-    (acc: Options, k: keyof Options): unknown => {
-      const opt = options[k];
-      if (typeof opt === "undefined") {
-        return { ...acc, [k]: DEFAULT_OPTIONS[k] };
-      }
-      return { ...acc, [k]: opt };
-    },
-    {}
-  ) as Options;
+  const opts: Options = {
+    ...DEFAULT_OPTIONS,
+    ...options
+  };
   const basicResult = printBasicValue(val, opts);
   if (basicResult !== null) {
     return basicResult;
diff --git a/testing/mod.ts b/testing/mod.ts
index fab8145e8..4ec241c20 100644
--- a/testing/mod.ts
+++ b/testing/mod.ts
@@ -54,7 +54,7 @@ interface TestStats {
 
 interface TestResult {
   name: string;
-  error: Error;
+  error?: Error;
   ok: boolean;
   printed: boolean;
 }
@@ -68,7 +68,7 @@ function createTestResults(tests: TestDefinition[]): TestResults {
   return tests.reduce(
     (acc: TestResults, { name }: TestDefinition, i: number): TestResults => {
       acc.keys.set(name, i);
-      acc.cases.set(i, { name, printed: false, ok: false, error: null });
+      acc.cases.set(i, { name, printed: false, ok: false, error: undefined });
       return acc;
     },
     { cases: new Map(), keys: new Map() }
@@ -114,11 +114,11 @@ function printResults(
 }
 
 function previousPrinted(name: string, results: TestResults): boolean {
-  const curIndex: number = results.keys.get(name);
+  const curIndex: number = results.keys.get(name)!;
   if (curIndex === 0) {
     return true;
   }
-  return results.cases.get(curIndex - 1).printed;
+  return results.cases.get(curIndex - 1)!.printed;
 }
 
 async function createTestCase(
@@ -127,7 +127,7 @@ async function createTestCase(
   exitOnFail: boolean,
   { fn, name }: TestDefinition
 ): Promise<void> {
-  const result: TestResult = results.cases.get(results.keys.get(name));
+  const result: TestResult = results.cases.get(results.keys.get(name)!)!;
   try {
     await fn();
     stats.passed++;
diff --git a/testing/pretty.ts b/testing/pretty.ts
index b2ab79d70..f471bd6fd 100644
--- a/testing/pretty.ts
+++ b/testing/pretty.ts
@@ -38,7 +38,7 @@ function createSign(diffType: DiffType): string {
 }
 
 function buildMessage(diffResult: ReadonlyArray<DiffResult<string>>): string[] {
-  const messages = [];
+  const messages: string[] = [];
   messages.push("");
   messages.push("");
   messages.push(