The second part of the first statement in the Zebra Problem says, "each [house] with a front door of a different colour".
Let's write a test for that.
But how? When I get stuck, I use a whiteboard.
So, it looks like our houses need an ID as a way to identify them. Next, they need a DoorColor property.
Let's select the house ID of the homes with the same DoorColor using LINQ.
Since both tests need an instance of ZebraProblem, I made it a private property and instantiated it in a SetUp method.
LINQ is a great query language to use get information from a collection. Let's talk about the LINQ statement.
For each house in the Zebra Problem, grab a house and assert that all the other houses in the Zebra Problem don't have the same color door.
If you find a house with the same color, stop, and write out a helpful message with the ID.
We can't compile because our House object does not have an Id or a DoorColor property. Let's add them.
You could make DoorColor a string, but then you have to deal with "Gray" vs. "Grey". It would be better if it was an enumeration.
We can compile, let's run the test.
1 test failed "A house was found with the same color door as house 0. Expected: 1 But was: 5"
There's a house with the same color door as house 0. We only expected 1 house to have the door color, but there was 5.
As soon as the test encounters a house door color count of more than 1, it stops. We have not assigned ID's to the homes yet, so the first house is ID 0. We have not given the homes a door color yet, so all 5 have the same color.
Let's read ahead in the problem and identify all the possible door colors. Then we can add them to our enumeration.
To get the test to pass we need to assign each house a unique door color.
Let's run the tests again.
2 tests passed
If you change one of the door colors to be same and run the test again, you get something like this:
1 test failed "A house was found with the same color door as house 0. Expected: 1 But was: 2"
All of the homes have an ID of 0. Let's write a test and fix this.
Let's run the test.
1 test failed "A house was found with the same ID as house 0. Expected: 1 But was: 5"
Now we assign each house a unique ID.
Let's run the tests.
3 tests passed