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Fix Custom Failure Messages article
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@jimweirich
jimweirich committed Dec 20, 2013
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114 changes: 49 additions & 65 deletions doc/article/custom_error_messages.md
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Expand Up @@ -26,50 +26,40 @@ Assuming that the <code>html_content</code> method is incomplete and
not yet marking emphasized text, the failure message from the
specification will be:

<pre>
1) Page content conversion to HTML
Failure/Error: Then { page.html_content == "Have a <em>nice</em> day." }
Then expression failed at .../spec/models/page_spec.rb:38
expected: "Have a _nice_ day."
to equal: "Have a <em>nice</em> day."
false <- page.html_content == "Have a <em>nice</em> day."
"Have a _nice_ day."
<- page.html_content
#<Page name: "HomePage", content: "Have a _nice_ day." ...>
<- page
# ./spec/models/page_spec.rb:38:in `block in Then'
</pre>
1) Page content conversion to HTML
Failure/Error: Then { page.html_content == "Have a <em>nice</em> day." }
Then expression failed at .../spec/models/page_spec.rb:38
expected: "Have a _nice_ day."
to equal: "Have a <em>nice</em> day."
false <- page.html_content == "Have a <em>nice</em> day."
"Have a _nice_ day."
<- page.html_content
#<Page name: "HomePage", content: "Have a _nice_ day." ...>
<- page
# ./spec/models/page_spec.rb:38:in `block in Then'

Let's break that down:

**It says what failed:**

<pre>
Failure/Error: Then { page.html_content == "Have a <em>nice</em> day." }
</pre>
Failure/Error: Then { page.html_content == "Have a <em>nice</em> day." }

**It says where it failed:**

<pre>
hen expression failed at .../spec/models/page_spec.rb:38
</pre>
Then expression failed at .../spec/models/page_spec.rb:38

**It says what was expected:**

<pre>
expected: "Have a _nice_ day."
to equal: "Have a <em>nice</em> day."
</pre>
expected: "Have a _nice_ day."
to equal: "Have a <em>nice</em> day."

**It then breaks down each subexpression and displays its value:**

<pre>
false <- page.html_content == "Have a <em>nice</em> day."
"Have a _nice_ day."
<- page.html_content
#<Page name: "HomePage", content: "Have a _nice_ day." ...>
<- page
</pre>
false <- page.html_content == "Have a <em>nice</em> day."
"Have a _nice_ day."
<- page.html_content
#<Page name: "HomePage", content: "Have a _nice_ day." ...>
<- page

All of this happens without the developer needing to write any special
error matchers or custom output. Everything you need to debug a spec
Expand Down Expand Up @@ -137,20 +127,18 @@ for presence. The failure message clearly tells you that the spec
failed because no error messages on the <code>name</code> field
mentioned 'blank'.

<pre>
1) Page validations with missing name
Failure/Error: Then { page.invalid? }
And expression failed at ./spec/models/page_spec.rb:27
Failing expression: And { page.errors[:name].any? { |msg| msg =~ /blank/ } }
false <- page.errors[:name].any? { |msg| msg =~ /blank/ }
["is not a wiki name"]
<- page.errors[:name]
#<ActiveModel::Errors:... @messages={:name=>["is not a wiki name"]}>
<- page.errors
#<Page name: nil, content: "CONTENT", ...>
<- page
# ./spec/models/page_spec.rb:25:in `block in Then'
</pre>
1) Page validations with missing name
Failure/Error: Then { page.invalid? }
And expression failed at ./spec/models/page_spec.rb:27
Failing expression: And { page.errors[:name].any? { |msg| msg =~ /blank/ } }
false <- page.errors[:name].any? { |msg| msg =~ /blank/ }
["is not a wiki name"]
<- page.errors[:name]
#<ActiveModel::Errors:... @messages={:name=>["is not a wiki name"]}>
<- page.errors
#<Page name: nil, content: "CONTENT", ...>
<- page
# ./spec/models/page_spec.rb:25:in `block in Then'

We get informative error messages, which is exactly what we want.

Expand Down Expand Up @@ -180,15 +168,13 @@ But there is a downside. Because <code>invalid?</code> only returns
true/false, and there are no mention of the <code>errors</code> object
in the Then clause, the failure message is really uninformative:

<pre>
1) Page validations with missing name
Failure/Error: Then { invalid_on(page, :name, /blank/) }
Then expression failed at ./spec/models/page_spec.rb:31
false <- invalid_on(page, :name, /blank/)
#<Page name: nil, content: "CONTENT", ...>
<- page
# ./spec/models/page_spec.rb:31:in `block in Then'
</pre>
1) Page validations with missing name
Failure/Error: Then { invalid_on(page, :name, /blank/) }
Then expression failed at ./spec/models/page_spec.rb:31
false <- invalid_on(page, :name, /blank/)
#<Page name: nil, content: "CONTENT", ...>
<- page
# ./spec/models/page_spec.rb:31:in `block in Then'

All we know is that the page is invalid. We get no indication of what
fields were actually in error and what the error messages actually
Expand Down Expand Up @@ -277,18 +263,16 @@ The failure message returned by <code>MustBeInvalid</code> is once
again clear and to the point. It contains all the information needed
for debugging.

<pre>
1) Page validations with missing name
Failure/Error: Then { must_be_invalid(page, :name, /blank/) }
Then expression failed at ./spec/models/page_spec.rb:31
Page had no errors matching (?-mix:blank) on field name
Errors were:
* Name is not a wiki name
<- must_be_invalid(page, :name, /blank/)
#<Page name: nil, content: "CONTENT", ...>
<- page
# ./spec/models/page_spec.rb:31:in `block in Then'
</pre>
1) Page validations with missing name
Failure/Error: Then { must_be_invalid(page, :name, /blank/) }
Then expression failed at ./spec/models/page_spec.rb:31
Page had no errors matching (?-mix:blank) on field name
Errors were:
* Name is not a wiki name
<- must_be_invalid(page, :name, /blank/)
#<Page name: nil, content: "CONTENT", ...>
<- page
# ./spec/models/page_spec.rb:31:in `block in Then'

## Summary

Expand Down

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