Customizable description

README.md

@@ -72,6 +72,51 @@ describe "plus" do
     end
   end
 end
+
+# It's also possible to override each combination name using magic variable :case_name
+# Output:
+# Custom test case name
+#   positive integers
+#     should do additions
+#   negative integers
+#     should do additions
+#   mixed integers
+#     should do additions
+describe "Custom names for regular syntax" do
+  where(:case_name, :a, :b, :answer) do
+    [
+      ["positive integers",  6,  2,  8],
+      ["negative integers", -1, -2, -3],
+      [   "mixed integers", -5,  3, -2],
+    ]
+  end
+
+  with_them do
+    it "should do additions" do
+      expect(a + b).to eq answer
+  end
+end
+
+# Or :case_names lambda for hash syntax
+# Output:
+# when hash arguments
+#   1 + 5 + 2
+#     sum is even
+#   1 + 5 + 4
+#     sum is even
+#   1 + 7 + 2
+#     sum is even
+#   ...
+describe "Custom naming for hash syntax" do
+  where(case_names: ->(a, b, c){"#{a} + #{b} + #{c}"}, a: [1, 3], b: [5, 7, 9], c: [2, 4])
+
+  with_them do
+    it "sum is even" do
+      expect(a + b + c).to be_even
+    end
+  end
+end
+
 ```
 
 I was inspired by [udzura's mock](https://gist.github.com/1881139).

lib/rspec/parameterized.rb

@@ -40,11 +40,19 @@ def initialize(arg_names, &block)
       def where(*args, &b)
 
         if args.size == 1 && args[0].instance_of?(Hash)
+          naming_func = args.first.delete(:case_names)
           params = args[0]
           first, *rest = params.values
+          arg_names = params.keys
+          arg_values = first.product(*rest)
 
-          set_parameters(params.keys) {
-            first.product(*rest)
+          if naming_func && naming_func.respond_to?(:call)
+            arg_names << :case_name
+            arg_values.map! { |row| row << naming_func.call(*row) }
+          end
+
+          set_parameters(arg_names) {
+            arg_values
           }
         else
           set_parameters(args, &b)
@@ -99,7 +107,7 @@ def define_cases(parameter, *args, &block)
 
         param_sets.each do |param_set|
           pairs = [parameter.arg_names, param_set].transpose.to_h
-          pretty_params = pairs.map {|name, val| "#{name}: #{params_inspect(val)}"}.join(", ")
+          pretty_params = pairs.has_key?(:case_name) ? pairs[:case_name] : pairs.map {|name, val| "#{name}: #{params_inspect(val)}"}.join(", ")
           describe(pretty_params, *args) do
             pairs.each do |name, val|
               let(name) { val }

spec/parametarized_spec.rb

@@ -66,6 +66,66 @@
     end
   end
 
+  describe "Custom test case name" do
+    context "when regular arguments" do
+      where(:case_name, :a, :b, :answer) do
+        [
+          ["positive integers",  6,  2,  8],
+          ["negative integers", -1, -2, -3],
+          [   "mixed integers", -5,  3, -2],
+        ]
+      end
+
+      with_them do
+        it "should do additions" do
+          expect(a + b).to eq answer
+        end
+
+        it "should have custom test name" do |example|
+          expect(example.metadata[:example_group][:description]).to eq case_name
+        end
+      end
+    end
+
+    context "when hash arguments" do
+      where(case_names: ->(a, b, c){"#{a} + #{b} + #{c}"}, a: [1, 3], b: [5, 7, 9], c: [2, 4])
+
+      with_them do
+        it "sum is even" do
+          expect(a + b + c).to be_even
+        end
+
+        it "should have custom names" do |example|
+          expect(example.metadata[:example_group][:description]).to include "+"
+        end
+      end
+    end
+
+    if RUBY_VERSION >= "2,1"
+      context "when arguments are separated with pipe (using TableSyntax)" do
+        using RSpec::Parameterized::TableSyntax
+
+        where(:case_name, :a, :b, :answer) do
+          "integers"      | 1                     | 2                     | 3
+          "strings"       | "hello "              | "world"               | "hello world"
+          "arrays"        | [1, 2, 3]             | [4, 5, 6]             | [1, 2, 3, 4, 5, 6]
+          "giant numbers" | 100000000000000000000 | 100000000000000000000 | 200000000000000000000
+        end
+
+        with_them do
+          it "a plus b is answer" do
+            expect(a + b).to eq answer
+          end
+
+          it "should have custom test name" do |example|
+            expect(example.metadata[:example_group][:description]).to eq case_name
+          end
+        end
+      end
+    end
+
+  end
+
   if RUBY_VERSION >= "2.1"
     describe "table separated with pipe (using TableSyntax)" do
       using RSpec::Parameterized::TableSyntax