Issue #756 Return warning message from BecauseOf when the phrase cann…

…ot be formatted (#764)
fluentassertions · Feb 15, 2018 · c493c4a · c493c4a
1 parent 6d49c00
commit c493c4a
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Showing 2 changed files with 29 additions and 6 deletions.
diff --git a/Src/FluentAssertions/Execution/AssertionScope.cs b/Src/FluentAssertions/Execution/AssertionScope.cs
@@ -115,18 +115,26 @@ public AssertionScope UsingLineBreaks
         /// <param name="because">
         /// A formatted phrase compatible with <see cref="string.Format(string,object[])"/> explaining why 
         /// the condition should be satisfied. If the phrase does not start with the word <i>because</i>, 
-        /// it is prepended to the message. 
+        /// it is prepended to the message. If the format of <paramref name="because"/> or 
+        /// <paramref name="becauseArgs"/> is not compatible with <see cref="string.Format(string,object[])"/>,
+        /// then a warning message is returned instead.
         /// </param>
         /// <param name="becauseArgs">
         /// Zero or more values to use for filling in any <see cref="string.Format(string,object[])"/> compatible placeholders.
         /// </param>
-        /// <exception cref="System.FormatException">
-        /// Thrown if the format of <paramref name="because"/> or <paramref name="becauseArgs"/> is not 
-        /// compatible with <see cref="string.Format(string,object[])"/>.
-        /// </exception>
         public AssertionScope BecauseOf(string because, params object[] becauseArgs)
         {
-            reason = () => string.Format(because ?? "", becauseArgs ?? new object[0]);
+            reason = () =>
+            {
+                try
+                {
+                    return string.Format(because ?? "", becauseArgs ?? new object[0]);
+                }
+                catch (FormatException formatException)
+                {
+                    return $"**WARNING** because message '{because}' could not be formatted with string.Format{Environment.NewLine}{formatException.StackTrace}";
+                }
+            };
             return this;
         }
 

diff --git a/Tests/Shared.Specs/AssertionScopeSpecs.cs b/Tests/Shared.Specs/AssertionScopeSpecs.cs
@@ -192,6 +192,21 @@ public void When_parentheses_are_used_in_the_because_arguments_it_should_render_
                 .WithMessage("*because can't use these in becauseArgs: { }*");
         }
 
+        [Fact]
+        public void When_invalid_format_is_used_in_because_parameter_it_should_render_default_text()
+        {
+            //-----------------------------------------------------------------------------------------------------------
+            // Act
+            //-----------------------------------------------------------------------------------------------------------
+            Action act = () => 1.Should().Be(2, "use of {} is considered invalid in because parameter");
+
+            //-----------------------------------------------------------------------------------------------------------
+            // Assert
+            //-----------------------------------------------------------------------------------------------------------
+            act.Should().Throw<XunitException>()
+                .WithMessage("*because message 'use of {} is considered invalid in because parameter' could not be formatted with string.Format*");
+        }
+
         [Fact]
         public void When_an_assertion_fails_in_a_scope_with_braces_it_should_use_the_name_as_the_assertion_context()
         {