Raise error for unknown column names

When specifying a non-existing column name in the expected result set,
this would be silently ignored. This would be confusing in case of typos
because they could lead to tests succeeding even in the face of errors.

This commit adds some additional checks in order to provide a more
meaningful error message when the returned result is empty, and to flag
typos immediately.

Fixes #18

Author: moertel

lib/squcumber-postgres/step_definitions/common_steps.rb

@@ -113,6 +113,8 @@
   expected = data.hashes || []
   expected = convert_mock_values(expected) if placeholder
 
+  sanity_check_result(actual, expected)
+
   expected.each_with_index do |hash, i|
     raise("Does not start with expected result, got:\n#{format_error(data, actual)}") unless actual[i].all? do |key, value|
       values_match(value, hash[key]) # actual,expected
@@ -125,10 +127,12 @@
   expected = data.hashes || []
   expected = convert_mock_values(expected) if placeholder
 
+  sanity_check_result(actual, expected)
+
   expected.each do |hash|
     raise("Result is not included, got:\n#{format_error(data, actual)}") unless actual.any? do |row|
       row.all? do |key, value|
-        values_match(value, hash[key]) # actual,expected
+        values_match(value, hash[key]) # actual, expected
       end
     end
   end
@@ -139,6 +143,8 @@
   expected = data.hashes || []
   expected = convert_mock_values(expected) if placeholder
 
+  sanity_check_result(actual, expected)
+
   expected.each do |hash|
     raise("Result is included, got:\n#{format_error(data, actual)}") if actual.any? do |row|
       row.all? do |key, value|
@@ -153,6 +159,8 @@
   expected = data.hashes || []
   expected = convert_mock_values(expected) if placeholder
 
+  sanity_check_result(actual, expected)
+
   raise("Does not match exactly, got:\n#{format_error(data, actual)}") if actual.length != expected.length
 
   actual.each_with_index do |row, i|

lib/squcumber-postgres/support/matchers.rb

@@ -1,4 +1,15 @@
 module MatcherHelpers
+  def sanity_check_result(actual, expected)
+    raise("The returned result is empty") if actual.empty?
+    raise("No data provided for comparison") if expected.empty?
+
+    expected[0].keys.each do |expected_key|
+      unless actual[0].keys.include?(expected_key)
+        raise("Column name '#{expected_key}' does not exist in result.\nAvailable column names are #{actual[0].keys.join(', ')}")
+      end
+    end
+  end
+
   def values_match(actual, expected)
     if expected.eql?('today')
       actual.match(/#{Regexp.quote(Date.today.to_s)}/)