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Visual Studio created one test method for
each public method in the point class.

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But in reality, we'll usually have
more than one test method for

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each method in the target.

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We treat each test method as a test case.

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For example, we created a test for
the distance to method for

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the distance between (0, 0) and (3, 4).

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However this is just one possible case.

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There are countless other
scenarios we could test.

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We can't possibly make tests for
every combination of points.

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This is where our good judgment comes in.

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I find it best to break up
the scenarios into groups and

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then write one or
two tests for each group.

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If the test for
a group of scenarios passes,

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then I can extrapolate that the code will
work for all the scenarios in that group.

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For example one group of tests could be
points that are horizontally aligned,

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another group are vertically
aligned points.

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Another are points that
are diagonal from each other.

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There's also the case where two
points are in the same position.

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These are some of the basic cases.

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We also need to think about edge cases.

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Edge cases are cases when the input
parameters are at the extreme

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end of what the code should accept.

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For example, we could test what happens
when a point is passed in whose x and

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y values are the maximum values for
what can be stored in an integer.

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In addition to edge cases
we can have corner cases.

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Corner cases are cases that
shouldn't normally happen but

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we need to make sure that the code handles
it gracefully if it's expected to.

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Things like what happens if null is passed
in or a point with negative x or y values.

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We often learn the most about our code
when considering edge or corner cases.

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That said, we also need to use our
judgement regarding the practicality of

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many of these tests.

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After all,

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distance too is a single line method
that does a straightforward computation.

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Three or four tests should be enough to
prove that it's implemented correctly.

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For example, we could assume that if
the method is able to accurately compute

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the distance to a point where both
the x and y values are different.

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Then it can also do so when only the x or
y value are different.

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It comes down to our comfort level
with making that assumption.

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Experience with testing helps too.

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At the very least, let's write
another test that verifies that

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two points in the same location
have a distance of zero.

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We'll write another test
of the DistanceTo method.

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We'll need to name this something
different than DistanceToTest

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since we already have
a method with that name.

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We can name it whatever we want.

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There are a number of different
conventions that folks

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use when creating test names.

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Since no one actually has to call these
methods, we can make the names for

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test methods longer
than we normally would.

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I prefer to name test methods so that they
describe the case that they're testing.

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Another convention is to put the name of
the method that's being tested first,

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followed by an underscore and
the name of the test case.

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This is fine, many test cases
are testing the behavior of the unit and

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not just the results of calling
a single method though.

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The important thing is that test cases can
be distinguished from each other based on

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what they're testing by
looking at their name.

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So I'll name this new test
DistanceToPointAtSamePosition.

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So I'll say Fact, then public void

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DistanceToPointAtSamePosition.

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For this test, let's just go ahead and
copy what we already wrote for

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the previous test.

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We'll make both the point and
the target the same place.

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So I'll say (3, 4) and the expected
distance between them should be (0, 0).

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So there you go.

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That's all we need for this test.

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I'll change the name of the other
method to something like DistanceTo,

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WithPythagoreanTriple, because 3, 4, and

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5 are whole numbers that form
the sides of a right triangle.

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Otherwise known as a Pythagorean triple.

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We could write a couple more test
cases for the Point class but

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I'll leave that up to you so
we can move on.