Add a true assertion and assertion test file.

source/test.ts

@@ -27,6 +27,16 @@ export class TestContext {
       title,
     );
   }
+
+  /** Assert that the value is true. */
+  true(actual: boolean, title?: string): void {
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-boolean-literal-compare
+    if (actual === true) {
+      return;
+    }
+
+    throw new AssertionError("Failed true assertion", actual, true, title);
+  }
 }
 
 /** Special options for test cases. */

tests/assertions.ts

@@ -0,0 +1,14 @@
+import {setup} from "../source/index.js";
+
+await setup("Assertions", async (group) => {
+  group.test("equals", async (test) => {
+    test.equals(true, true, "boolean");
+    test.equals(Math.PI, Math.PI, "number");
+    test.equals("A string!", "A string!", "string");
+  });
+
+  group.test("true", async (test) => {
+    test.true(1 > 0, "logic");
+    test.true(new Date() instanceof Date, "instanceof");
+  });
+});

tests/index.ts

@@ -1,5 +1,7 @@
 import {setup} from "../source/index.js";
 
+await import("./assertions.js");
+
 async function add(a: number, b: number): Promise<number> {
   await new Promise<void>((resolve) => {
     setTimeout(() => {