Add a false assertion.

source/test.ts

@@ -28,6 +28,16 @@ export class TestContext {
     );
   }
 
+  /** Assert that the value is false. */
+  false(actual: boolean, title?: string): void {
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-boolean-literal-compare
+    if (actual === false) {
+      return;
+    }
+
+    throw new AssertionError("Failed false assertion", actual, false, title);
+  }
+
   /** Assert that the value is true. */
   true(actual: boolean, title?: string): void {
     // eslint-disable-next-line @typescript-eslint/no-unnecessary-boolean-literal-compare

tests/assertions.ts

@@ -7,6 +7,11 @@ await setup("Assertions", async (group) => {
     test.equals("A string!", "A string!", "string");
   });
 
+  group.test("false", async (test) => {
+    test.false(1 < 0, "logic");
+    test.false(new Date() instanceof String, "instanceof");
+  });
+
   group.test("true", async (test) => {
     test.true(1 > 0, "logic");
     test.true(new Date() instanceof Date, "instanceof");