Move CredentialTests to TokenEndpointTests where appropriate, improve…

… constructors by throwing exception when null is provided as argument

src/RobinTTY.NordigenApiClient.Tests/LiveApi/CredentialTests.cs

@@ -25,22 +25,6 @@ public async Task MakeRequestWithInvalidCredentials()
             "0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef");
         var apiClient = new NordigenClient(httpClient, invalidCredentials);
 
-        // Returns BasicError
-        var agreementsResponse = await apiClient.AgreementsEndpoint.GetAgreements(10, 0);
-        Assert.Multiple(() =>
-        {
-            Assert.That(agreementsResponse.StatusCode, Is.EqualTo(HttpStatusCode.Unauthorized));
-            AssertErrorMatchesExpectation(agreementsResponse.Error!);
-        });
-
-        // Returns InstitutionsError
-        var institutionResponse = await apiClient.InstitutionsEndpoint.GetInstitutions();
-        Assert.Multiple(() =>
-        {
-            Assert.That(institutionResponse.StatusCode, Is.EqualTo(HttpStatusCode.Unauthorized));
-            AssertErrorMatchesExpectation(institutionResponse.Error!);
-        });
-
         // Returns AccountsError
         var balancesResponse = await apiClient.AccountsEndpoint.GetBalances(_secrets[9]);
         Assert.Multiple(() =>

src/RobinTTY.NordigenApiClient.Tests/LiveApi/Endpoints/TokenEndpointTests.cs

@@ -70,4 +70,26 @@ public async Task ReuseExpiredToken()
         var result = await apiClient.RequisitionsEndpoint.GetRequisitions(10, 0);
         AssertionHelpers.AssertNordigenApiResponseIsSuccessful(result, HttpStatusCode.OK);
     }
+
+    /// <summary>
+    /// Tests the failure of authentication when trying to get a new token pair.
+    /// </summary>
+    [Test]
+    public async Task GetTokenPairWithInvalidCredentials()
+    {
+        using var httpClient = new HttpClient();
+        var invalidCredentials = new NordigenClientCredentials("01234567-89ab-cdef-0123-456789abcdef",
+            "0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef");
+        var apiClient = new NordigenClient(httpClient, invalidCredentials);
+
+        // Returns BasicError
+        var agreementsResponse = await apiClient.AgreementsEndpoint.GetAgreements(10, 0);
+        Assert.Multiple(() =>
+        {
+            Assert.That(agreementsResponse.StatusCode, Is.EqualTo(HttpStatusCode.Unauthorized));
+            AssertionHelpers.AssertNordigenApiResponseIsUnsuccessful(agreementsResponse, HttpStatusCode.Unauthorized);
+            AssertionHelpers.AssertBasicResponseMatchesExpectations(agreementsResponse.Error, "Authentication failed",
+                "No active account found with the given credentials");
+        });
+    }
 }

src/RobinTTY.NordigenApiClient/Models/Jwt/JsonWebTokenPair.cs

@@ -42,8 +42,8 @@ public class JsonWebTokenPair
     [JsonConstructor]
     public JsonWebTokenPair(JsonWebToken accessToken, JsonWebToken refreshToken, int accessExpires, int refreshExpires)
     {
-        AccessToken = accessToken;
-        RefreshToken = refreshToken;
+        AccessToken = accessToken ?? throw new ArgumentNullException(nameof(accessToken));
+        RefreshToken = refreshToken ?? throw new ArgumentNullException(nameof(refreshToken));
         AccessExpires = accessExpires;
         RefreshExpires = refreshExpires;
     }

src/RobinTTY.NordigenApiClient/Models/NordigenClientCredentials.cs

@@ -26,7 +26,7 @@ public class NordigenClientCredentials
     /// <param name="secretKey">Secret Nordigen key.</param>
     public NordigenClientCredentials(string secretId, string secretKey)
     {
-        SecretId = secretId;
-        SecretKey = secretKey;
+        SecretId = secretId ?? throw new ArgumentNullException(nameof(secretId));
+        SecretKey = secretKey ?? throw new ArgumentNullException(nameof(secretKey));
     }
 }