diff --git a/MultiversalDiplomacy/Adjudicate/OrderValidation.cs b/MultiversalDiplomacy/Adjudicate/OrderValidation.cs
index 553e47c..7b2afe2 100644
--- a/MultiversalDiplomacy/Adjudicate/OrderValidation.cs
+++ b/MultiversalDiplomacy/Adjudicate/OrderValidation.cs
@@ -27,6 +27,16 @@ public class OrderValidation
         this.Order = order;
         this.Valid = valid;
         this.Reason = reason;
+
+        if (this.Valid != (this.Reason == ValidationReason.Valid))
+        {
+            throw new ArgumentException("Only valid orders should have the Valid reason");
+        }
+    }
+
+    public override string ToString()
+    {
+        return this.Valid ? "Valid" : $"Invalid ({this.Reason})";
     }
 }
 
diff --git a/MultiversalDiplomacyTests/Is.cs b/MultiversalDiplomacyTests/Is.cs
new file mode 100644
index 0000000..5e36e88
--- /dev/null
+++ b/MultiversalDiplomacyTests/Is.cs
@@ -0,0 +1,12 @@
+using MultiversalDiplomacy.Adjudicate;
+
+namespace MultiversalDiplomacyTests;
+
+public class Is : NUnit.Framework.Is
+{
+    public static OrderValidationConstraint Valid
+        => new OrderValidationConstraint(true, ValidationReason.Valid);
+
+    public static OrderValidationConstraint Invalid(ValidationReason expected)
+        => new OrderValidationConstraint(false, expected);
+}
diff --git a/MultiversalDiplomacyTests/MovementAdjudicatorTest.cs b/MultiversalDiplomacyTests/MovementAdjudicatorTest.cs
index 8c81001..ec23950 100644
--- a/MultiversalDiplomacyTests/MovementAdjudicatorTest.cs
+++ b/MultiversalDiplomacyTests/MovementAdjudicatorTest.cs
@@ -17,15 +17,8 @@ public class MovementAdjudicatorTest
 
         setup.ValidateOrders(new MovementPhaseAdjudicator());
 
-        Assert.Multiple(() =>
-        {
-            Assert.That(order.Validation.Valid, Is.True, "Unexpected validation result");
-            Assert.That(
-                order.Validation.Reason,
-                Is.EqualTo(ValidationReason.Valid),
-                "Unexpected validation reason");
-            Assert.That(order.Replacement, Is.Null, "Unexpected order replacement");
-        });
+        Assert.That(order.Validation, Is.Valid, "Unexpected validation result");
+        Assert.That(order.Replacement, Is.Null, "Unexpected order replacement");
     }
 
     [Test]
@@ -37,15 +30,8 @@ public class MovementAdjudicatorTest
 
         setup.ValidateOrders(new MovementPhaseAdjudicator());
 
-        Assert.Multiple(() =>
-        {
-            Assert.That(order.Validation.Valid, Is.True, "Unexpected validation result");
-            Assert.That(
-                order.Validation.Reason,
-                Is.EqualTo(ValidationReason.Valid),
-                "Unexpected validation reason");
-            Assert.That(order.Replacement, Is.Null, "Unexpected order replacement");
-        });
+        Assert.That(order.Validation, Is.Valid, "Unexpected validation result");
+        Assert.That(order.Replacement, Is.Null, "Unexpected order replacement");
     }
 
     [Test]
@@ -57,15 +43,8 @@ public class MovementAdjudicatorTest
 
         setup.ValidateOrders(new MovementPhaseAdjudicator());
 
-        Assert.Multiple(() =>
-        {
-            Assert.That(order.Validation.Valid, Is.True, "Unexpected validation result");
-            Assert.That(
-                order.Validation.Reason,
-                Is.EqualTo(ValidationReason.Valid),
-                "Unexpected validation reason");
-            Assert.That(order.Replacement, Is.Null, "Unexpected order replacement");
-        });
+        Assert.That(order.Validation, Is.Valid, "Unexpected validation result");
+        Assert.That(order.Replacement, Is.Null, "Unexpected order replacement");
     }
 
     [Test]
@@ -77,15 +56,8 @@ public class MovementAdjudicatorTest
 
         setup.ValidateOrders(new MovementPhaseAdjudicator());
 
-        Assert.Multiple(() =>
-        {
-            Assert.That(order.Validation.Valid, Is.True, "Unexpected validation result");
-            Assert.That(
-                order.Validation.Reason,
-                Is.EqualTo(ValidationReason.Valid),
-                "Unexpected validation reason");
-            Assert.That(order.Replacement, Is.Null, "Unexpected order replacement");
-        });
+        Assert.That(order.Validation, Is.Valid, "Unexpected validation result");
+        Assert.That(order.Replacement, Is.Null, "Unexpected order replacement");
     }
 
     [Test]
@@ -97,14 +69,7 @@ public class MovementAdjudicatorTest
 
         setup.ValidateOrders(new MovementPhaseAdjudicator());
 
-        Assert.Multiple(() =>
-        {
-            Assert.That(order.Validation.Valid, Is.True, "Unexpected validation result");
-            Assert.That(
-                order.Validation.Reason,
-                Is.EqualTo(ValidationReason.Valid),
-                "Unexpected validation reason");
-            Assert.That(order.Replacement, Is.Null, "Unexpected order replacement");
-        });
+        Assert.That(order.Validation, Is.Valid, "Unexpected validation result");
+        Assert.That(order.Replacement, Is.Null, "Unexpected order replacement");
     }
-}
\ No newline at end of file
+}
diff --git a/MultiversalDiplomacyTests/OrderValidationConstraint.cs b/MultiversalDiplomacyTests/OrderValidationConstraint.cs
new file mode 100644
index 0000000..ece27bd
--- /dev/null
+++ b/MultiversalDiplomacyTests/OrderValidationConstraint.cs
@@ -0,0 +1,30 @@
+using MultiversalDiplomacy.Adjudicate;
+
+using NUnit.Framework.Constraints;
+
+namespace MultiversalDiplomacyTests;
+
+public class OrderValidationConstraint : Constraint
+{
+    private bool valid;
+    private ValidationReason expectedReason;
+
+    public override string Description
+    {
+        get => this.valid ? "Valid" : $"Invalid ({this.expectedReason})";
+    }
+
+    public OrderValidationConstraint(bool valid, ValidationReason expected)
+    {
+        this.valid = valid;
+        this.expectedReason = expected;
+    }
+
+    public override ConstraintResult ApplyTo<TActual>(TActual actual)
+    {
+        bool success = actual is OrderValidation validation
+            && validation.Valid == this.valid
+            && validation.Reason == this.expectedReason;
+        return new ConstraintResult(this, actual, success);
+    }
+}