diff --git a/tests/OnspringClient.spec.ts b/tests/OnspringClient.spec.ts
index 595c713..6c5142c 100644
--- a/tests/OnspringClient.spec.ts
+++ b/tests/OnspringClient.spec.ts
@@ -410,6 +410,100 @@ describe('OnspringClient', function () {
       expect(result.data).to.have.property('name', 'Test App 1');
     });
 
-    // TODO: Add test cases for 401, 403, and 404 status codes
+    it('should return a promise that resolves to an api response when request receives a 401 response', async function () {
+      const client = new OnspringClient(baseUrl, apiKey);
+
+      const mockAxiosClient = axios.create({
+        baseURL: baseUrl,
+        headers: {
+          'x-apikey': apiKey,
+          'x-api-version': '2',
+        },
+      });
+
+      sinon.stub(mockAxiosClient, 'get').returns(
+        Promise.resolve({
+          status: 401,
+          statusText: 'Unauthorized',
+          headers: {},
+          config: {} as InternalAxiosRequestConfig,
+        } as AxiosResponse)
+      );
+
+      sinon.stub(client, '_client' as any).value(mockAxiosClient);
+
+      const result = await client.getAppById(1);
+      expect(result).to.be.instanceOf(ApiResponse);
+      expect(result).to.have.property('statusCode', 401);
+      expect(result).to.have.property('isSuccessful', false);
+      expect(result.message).to.be.undefined;
+      expect(result.data).to.be.null;
+    });
+
+    it('should return a promise that resolves to an api response when request receives a 403 response', async function () {
+      const client = new OnspringClient(baseUrl, apiKey);
+
+      const mockAxiosClient = axios.create({
+        baseURL: baseUrl,
+        headers: {
+          'x-apikey': apiKey,
+          'x-api-version': '2',
+        },
+      });
+
+      sinon.stub(mockAxiosClient, 'get').returns(
+        Promise.resolve({
+          status: 403,
+          statusText: 'Unauthorized',
+          data: {
+            message: 'Client does not have access to read app: 1',
+          },
+          headers: {},
+          config: {} as InternalAxiosRequestConfig,
+        } as AxiosResponse)
+      );
+
+      sinon.stub(client, '_client' as any).value(mockAxiosClient);
+
+      const result = await client.getAppById(1);
+      expect(result).to.be.instanceOf(ApiResponse);
+      expect(result).to.have.property('statusCode', 403);
+      expect(result).to.have.property('isSuccessful', false);
+      expect(result).to.have.property(
+        'message',
+        'Client does not have access to read app: 1'
+      );
+      expect(result).to.have.property('data', null);
+    });
+
+    it('should return a promise that resolves to an api response when request receives a 404 response', async function () {
+      const client = new OnspringClient(baseUrl, apiKey);
+
+      const mockAxiosClient = axios.create({
+        baseURL: baseUrl,
+        headers: {
+          'x-apikey': apiKey,
+          'x-api-version': '2',
+        },
+      });
+
+      sinon.stub(mockAxiosClient, 'get').returns(
+        Promise.resolve({
+          status: 404,
+          statusText: 'Not Found',
+          headers: {},
+          config: {} as InternalAxiosRequestConfig,
+        } as AxiosResponse)
+      );
+
+      sinon.stub(client, '_client' as any).value(mockAxiosClient);
+
+      const result = await client.getAppById(1);
+      expect(result).to.be.instanceOf(ApiResponse);
+      expect(result).to.have.property('statusCode', 404);
+      expect(result).to.have.property('isSuccessful', false);
+      expect(result.message).to.be.undefined;
+      expect(result.data).to.be.null;
+    });
   });
 });