feat(core): Error type factories

packages/core/src/lib/helpers/TypeFactories.ts

@@ -2,6 +2,7 @@ import { ArrayAssertion } from "../ArrayAssertion";
 import { Assertion, Constructor } from "../Assertion";
 import { BooleanAssertion } from "../BooleanAssertion";
 import { DateAssertion } from "../DateAssertion";
+import { ErrorAssertion } from "../ErrorAssertion";
 import { type AnyFunction, FunctionAssertion } from "../FunctionAssertion";
 import { NumberAssertion } from "../NumberAssertion";
 import { ObjectAssertion } from "../ObjectAssertion";
@@ -47,6 +48,10 @@ export interface StaticTypeFactories {
    * A `Date` TypeFactory.
    */
   Date: TypeFactory<Date, DateAssertion>;
+  /**
+   * An `Error` TypeFactory.
+   */
+  Error: TypeFactory<Error, ErrorAssertion<Error>>;
   /**
    * A `function` TypeFactory.
    */
@@ -71,6 +76,20 @@ export interface StaticTypeFactories {
    * @param innerType the TypeFactory for the array type
    */
   array<T>(innerType?: TypeFactory<T, Assertion<T>>): TypeFactory<T[], ArrayAssertion<T>>;
+  /**
+   * Creates an `Error` TypeFactory for a specific error constructor.
+   *
+   * @example
+   * ```
+   * class CustomError extends Error { ... }
+   *
+   * TypeFactories.error(CustomError); // a `CustomError` error factory
+   * ```
+   *
+   * @typeParam T the type of the error constructor
+   * @param Type the error constructor
+   */
+  error<T extends Error>(Type: Constructor<T>): TypeFactory<T, ErrorAssertion<T>>;
   /**
    * Creates a TypeFactory for an instance of the given constructor.
    *
@@ -114,6 +133,11 @@ export const TypeFactories: Readonly<StaticTypeFactories> = {
     predicate: (value): value is Date => value instanceof Date,
     typeName: Date.name,
   },
+  Error: {
+    Factory: ErrorAssertion,
+    predicate: (value): value is Error => value instanceof Error,
+    typeName: Error.name,
+  },
   Function: {
     Factory: FunctionAssertion,
     predicate: (value): value is AnyFunction => typeof value === "function",
@@ -139,6 +163,13 @@ export const TypeFactories: Readonly<StaticTypeFactories> = {
       typeName: "array",
     };
   },
+  error<T extends Error>(Type: Constructor<T>) {
+    return {
+      Factory: ErrorAssertion,
+      predicate: (value): value is T => value instanceof Type,
+      typeName: Type.name,
+    };
+  },
   instanceOf<T>(type: Constructor<T>) {
     return {
       Factory: Assertion,

packages/core/test/lib/helpers/TypeFactories.test.ts

@@ -2,6 +2,17 @@ import { TypeFactories } from "../../../src/lib/helpers/TypeFactories";
 
 import assert from "assert";
 
+class CustomError extends Error {
+
+  public constructor(message?: string) {
+    super(message);
+
+    this.name = this.constructor.name;
+    Error.captureStackTrace(this, this.constructor);
+    Object.setPrototypeOf(this, CustomError.prototype);
+  }
+}
+
 describe("[Unit] TypeFactories.test.ts", () => {
   describe(".predicate", () => {
     describe("#Boolean", () => {
@@ -42,6 +53,24 @@ describe("[Unit] TypeFactories.test.ts", () => {
       });
     });
 
+    describe("#Error", () => {
+      context("when the value is an Error", () => {
+        it("returns true", () => {
+          const result = TypeFactories.Error.predicate(new Error("foo"));
+
+          assert.equal(result, true);
+        });
+      });
+
+      context("when the value is not an Error", () => {
+        it("returns false", () => {
+          const result = TypeFactories.Error.predicate("foo");
+
+          assert.equal(result, false);
+        });
+      });
+    });
+
     describe("#Function", () => {
       context("when the value is a function", () => {
         it("returns true", () => {
@@ -143,6 +172,24 @@ describe("[Unit] TypeFactories.test.ts", () => {
       });
     });
 
+    describe(".error", () => {
+      context("when the value is an instace o the error type", () => {
+        it("returns true", () => {
+          const result = TypeFactories.error(CustomError).predicate(new CustomError("foo"));
+
+          assert.equal(result, true);
+        });
+      });
+
+      context("when the value is not an instace o the error type", () => {
+        it("returns false", () => {
+          const result = TypeFactories.error(CustomError).predicate(new Error("foo"));
+
+          assert.equal(result, false);
+        });
+      });
+    });
+
     describe(".instanceOf", () => {
       context("when the value is an instance of the passed type", () => {
         it("returns true", () => {