diff --git a/dependency-manager.test.ts b/dependency-manager.test.ts
new file mode 100644
index 0000000..d628584
--- /dev/null
+++ b/dependency-manager.test.ts
@@ -0,0 +1,77 @@
+import {
+  assertEquals,
+  assertRejects,
+  assertThrows,
+} from "https://deno.land/std@0.224.0/assert/mod.ts";
+import { DependencyManager } from "./dependency-manager.ts";
+
+// Test case for registering a module
+Deno.test("DependencyManager: register a module", () => {
+  const manager = new DependencyManager();
+  const provider = () => "dependency";
+  manager.register("identifier", provider);
+  assertEquals(
+    manager.resolve("identifier"),
+    Promise.resolve("dependency"),
+  );
+});
+
+// Test case for resolving a module
+Deno.test("DependencyManager: resolve a module", async () => {
+  const manager = new DependencyManager();
+  const provider = () => "dependency";
+  manager.register("identifier", provider);
+  const result = await manager.resolve("identifier");
+  assertEquals(result, "dependency");
+});
+
+// Test case for resolving an async module
+Deno.test("DependencyManager: resolve an async module", async () => {
+  const manager = new DependencyManager();
+  const provider = () => {
+    return new Promise((resolve) =>
+      setTimeout(() => resolve("dependency"), 100)
+    );
+  };
+  manager.register("identifier", provider);
+  const result = await manager.resolve("identifier");
+  assertEquals(result, "dependency");
+});
+
+// Test case for handling circular dependencies
+Deno.test("DependencyManager: circular dependency detection", async () => {
+  const manager = new DependencyManager();
+  const providerA = async () => await manager.resolve("B");
+  const providerB = async () => await manager.resolve("A");
+
+  manager.register("A", providerA);
+  manager.register("B", providerB);
+
+  await assertRejects(
+    () => manager.resolve("A"),
+    Error,
+    "Circular dependency detected for module A.",
+  );
+});
+
+// Test case for handling duplicate module registration
+Deno.test("DependencyManager: duplicate module registration", () => {
+  const manager = new DependencyManager();
+  const provider = () => "dependency";
+  manager.register("identifier", provider);
+  assertThrows(
+    () => manager.register("identifier", provider),
+    Error,
+    "Module identifier is already registered.",
+  );
+});
+
+// Test case for handling unresolved modules
+Deno.test("DependencyManager: resolve an unregistered module", async () => {
+  const manager = new DependencyManager();
+  await assertRejects(
+    () => manager.resolve("unregistered-identifier"),
+    Error,
+    "Module unregistered-identifier is not registered.",
+  );
+});