diff --git a/Tests/VaporOAuthTests/AuthorizationTests/AuthorizationRequestTests.swift b/Tests/VaporOAuthTests/AuthorizationTests/AuthorizationRequestTests.swift
index 47e1f85..49d0ad8 100644
--- a/Tests/VaporOAuthTests/AuthorizationTests/AuthorizationRequestTests.swift
+++ b/Tests/VaporOAuthTests/AuthorizationTests/AuthorizationRequestTests.swift
@@ -6,8 +6,6 @@ class AuthorizationRequestTests: XCTestCase {
     // MARK: - Properties
 
     var app: Application!
-    /// used for some but not all tests
-    var customApp: Application?
     var fakeClientRetriever: FakeClientGetter!
     var capturingAuthoriseHandler: CapturingAuthoriseHandler!
 
@@ -35,7 +33,6 @@ class AuthorizationRequestTests: XCTestCase {
 
     override func tearDown() async throws {
         app.shutdown()
-        customApp?.shutdown()
         try await super.tearDown()
     }
 
@@ -224,7 +221,8 @@ class AuthorizationRequestTests: XCTestCase {
     }
 
     func testThatUnknownScopeReturnsInvalidScopeError() async throws {
-        customApp = try TestDataBuilder.getOAuth2Application(
+        app.shutdown()
+        app = try TestDataBuilder.getOAuth2Application(
             clientRetriever: fakeClientRetriever,
             authorizeHandler: capturingAuthoriseHandler,
             validScopes: ["email", "profile", "admin"]
@@ -234,8 +232,7 @@ class AuthorizationRequestTests: XCTestCase {
         let response = try await respondToOAuthRequest(
             clientID: clientID,
             redirectURI: redirectURI,
-            scope: invalidScope,
-            on: customApp!
+            scope: invalidScope
         )
 
         XCTAssertEqual(response.status, .seeOther)
@@ -295,7 +292,8 @@ class AuthorizationRequestTests: XCTestCase {
     }
 
     func testNonHTTPSRedirectURICanNotBeUsedWhenInProduction() async throws {
-        customApp = try TestDataBuilder.getOAuth2Application(
+        app.shutdown()
+        app = try TestDataBuilder.getOAuth2Application(
             clientRetriever: fakeClientRetriever,
             authorizeHandler: capturingAuthoriseHandler,
             environment: .production
@@ -309,7 +307,7 @@ class AuthorizationRequestTests: XCTestCase {
         )
         fakeClientRetriever.validClients[clientID] = httpClient
 
-        _ = try await respondToOAuthRequest(clientID: clientID, redirectURI: nonHTTPSRedirectURI, on: customApp!)
+        _ = try await respondToOAuthRequest(clientID: clientID, redirectURI: nonHTTPSRedirectURI)
 
         XCTAssertEqual(capturingAuthoriseHandler.authorizationError, .httpRedirectURI)
     }
@@ -372,11 +370,9 @@ class AuthorizationRequestTests: XCTestCase {
         clientID: String?,
         redirectURI: String?,
         scope: String? = nil,
-        state: String? = nil,
-        on customApp: Application? = nil
+        state: String? = nil
     ) async throws -> XCTHTTPResponse {
-        let app: Application! = customApp ?? self.app
-        return try await TestDataBuilder.getAuthRequestResponse(
+        try await TestDataBuilder.getAuthRequestResponse(
             with: app,
             responseType: responseType,
             clientID: clientID,
diff --git a/Tests/VaporOAuthTests/AuthorizationTests/AuthorizationResponseTests.swift b/Tests/VaporOAuthTests/AuthorizationTests/AuthorizationResponseTests.swift
index 78ec3e1..5a960f9 100644
--- a/Tests/VaporOAuthTests/AuthorizationTests/AuthorizationResponseTests.swift
+++ b/Tests/VaporOAuthTests/AuthorizationTests/AuthorizationResponseTests.swift
@@ -6,7 +6,6 @@ class AuthorizationResponseTests: XCTestCase {
     // MARK: - Properties
 
     var app: Application!
-    var customApp: Application?
     var fakeClientRetriever: FakeClientGetter!
     var capturingAuthoriseHandler: CapturingAuthoriseHandler!
     var fakeCodeManager: FakeCodeManager!
@@ -50,7 +49,6 @@ class AuthorizationResponseTests: XCTestCase {
 
     override func tearDown() async throws {
         app.shutdown()
-        customApp?.shutdown()
         try await super.tearDown()
     }
 
@@ -130,7 +128,9 @@ class AuthorizationResponseTests: XCTestCase {
     }
 
     func testThatRedirectURIMustBeHTTPSForProduction() async throws {
-        customApp = try TestDataBuilder.getOAuth2Application(
+        app.shutdown()
+
+        app = try TestDataBuilder.getOAuth2Application(
             clientRetriever: fakeClientRetriever,
             authorizeHandler: capturingAuthoriseHandler,
             environment: .production,
@@ -142,7 +142,7 @@ class AuthorizationResponseTests: XCTestCase {
         let newClient = OAuthClient(clientID: clientID, redirectURIs: [redirectURI], allowedGrantType: .authorization)
         fakeClientRetriever.validClients[clientID] = newClient
 
-        let response = try await getAuthResponse(clientID: clientID, redirectURI: redirectURI, on: customApp!)
+        let response = try await getAuthResponse(clientID: clientID, redirectURI: redirectURI)
 
         XCTAssertEqual(response.status, .badRequest)
     }
@@ -308,11 +308,9 @@ class AuthorizationResponseTests: XCTestCase {
         state: String? = nil,
         user: OAuthUser? = TestDataBuilder.anyOAuthUser(),
         csrfToken: String? = "the-csrf-token",
-        sessionID: String? = "the-session-ID",
-        on customApp: Application? = nil
+        sessionID: String? = "the-session-ID"
     ) async throws -> XCTHTTPResponse {
-        let app: Application! = customApp ?? self.app
-        return try await TestDataBuilder.getAuthResponseResponse(
+        try await TestDataBuilder.getAuthResponseResponse(
             with: app,
             approve: approve,
             clientID: clientID,
diff --git a/Tests/VaporOAuthTests/GrantTests/ImplicitGrantTests.swift b/Tests/VaporOAuthTests/GrantTests/ImplicitGrantTests.swift
index 88c77f2..36bb262 100644
--- a/Tests/VaporOAuthTests/GrantTests/ImplicitGrantTests.swift
+++ b/Tests/VaporOAuthTests/GrantTests/ImplicitGrantTests.swift
@@ -4,8 +4,6 @@ import XCTVapor
 class ImplicitGrantTests: XCTestCase {
     // MARK: - Properties
     var app: Application!
-    // used for some, but not all tests
-    var customApp: Application?
     var fakeClientGetter: FakeClientGetter!
     var fakeTokenManager: FakeTokenManager!
     var capturingAuthHandler: CapturingAuthoriseHandler!
@@ -51,7 +49,6 @@ class ImplicitGrantTests: XCTestCase {
 
     override func tearDown() async throws {
         app.shutdown()
-        customApp?.shutdown()
         try await super.tearDown()
     }
 
@@ -245,7 +242,8 @@ class ImplicitGrantTests: XCTestCase {
     }
 
     func testThatRedirectURIMustBeHTTPSForProduction() async throws {
-        customApp = try TestDataBuilder.getOAuth2Application(
+        app.shutdown()
+        app = try TestDataBuilder.getOAuth2Application(
             clientRetriever: fakeClientGetter,
             authorizeHandler: capturingAuthHandler,
             environment: .production,
@@ -257,7 +255,7 @@ class ImplicitGrantTests: XCTestCase {
         let newClient = OAuthClient(clientID: clientID, redirectURIs: [redirectURI], allowedGrantType: .implicit)
         fakeClientGetter.validClients[clientID] = newClient
 
-        let response = try await getImplicitGrantResponse(clientID: clientID, redirectURI: redirectURI, on: customApp!)
+        let response = try await getImplicitGrantResponse(clientID: clientID, redirectURI: redirectURI)
 
         XCTAssertEqual(response.status, .badRequest)
     }
@@ -352,7 +350,8 @@ class ImplicitGrantTests: XCTestCase {
         fakeTokenManager.accessTokenToReturn = accessToken
         let user = OAuthUser(userID: userID, username: "luke", emailAddress: "luke@skywalker.com", password: "obiwan")
 
-        customApp = try TestDataBuilder.getOAuth2Application(
+        app.shutdown()
+        app = try TestDataBuilder.getOAuth2Application(
             tokenManager: fakeTokenManager,
             clientRetriever: fakeClientGetter,
             authorizeHandler: capturingAuthHandler,
@@ -361,7 +360,7 @@ class ImplicitGrantTests: XCTestCase {
             registeredUsers: [user]
         )
 
-        _ = try await getImplicitGrantResponse(user: user, on: customApp!)
+        _ = try await getImplicitGrantResponse(user: user)
 
         guard let token = fakeTokenManager.getAccessToken(accessToken) else {
             XCTFail()
@@ -385,7 +384,8 @@ class ImplicitGrantTests: XCTestCase {
     }
 
     func testThatUserMustBeLoggedInWhenMakingImplicitTokenRequest() async throws {
-        customApp = try TestDataBuilder.getOAuth2Application(
+        app.shutdown()
+        app = try TestDataBuilder.getOAuth2Application(
             tokenManager: fakeTokenManager,
             clientRetriever: fakeClientGetter,
             authorizeHandler: capturingAuthHandler,
@@ -393,7 +393,7 @@ class ImplicitGrantTests: XCTestCase {
             sessions: fakeSessions
         )
 
-        let response = try await getImplicitGrantResponse(user: nil, on: customApp!)
+        let response = try await getImplicitGrantResponse(user: nil)
 
         XCTAssertEqual(response.status, .unauthorized)
     }
@@ -466,18 +466,9 @@ class ImplicitGrantTests: XCTestCase {
         clientID: String? = "ABCDEF",
         redirectURI: String? = "https://api.brokenhands.io/callback",
         scope: String? = nil,
-        state: String? = nil,
-        on customApp: Application? = nil
+        state: String? = nil
     ) async throws -> XCTHTTPResponse {
-        let app: Application! = customApp ?? self.app
-        return try await TestDataBuilder.getAuthRequestResponse(
-            with: app,
-            responseType: responseType,
-            clientID: clientID,
-            redirectURI: redirectURI,
-            scope: scope,
-            state: state
-        )
+        return try await TestDataBuilder.getAuthRequestResponse(with: app, responseType: responseType, clientID: clientID, redirectURI: redirectURI, scope: scope, state: state)
     }
 
     private func getImplicitGrantResponse(
@@ -489,10 +480,8 @@ class ImplicitGrantTests: XCTestCase {
         state: String? = nil,
         user: OAuthUser? = TestDataBuilder.anyOAuthUser(),
         csrfToken: String? = "the-csrf-token",
-        sessionID: String? = "the-session-ID",
-        on customApp: Application? = nil
+        sessionID: String? = "the-session-ID"
     ) async throws -> XCTHTTPResponse {
-        let app: Application! = customApp ?? self.app
         return try await TestDataBuilder.getAuthResponseResponse(
             with: app,
             approve: approve,