Add Predicate#assert!, with the help of minitest.

CHANGELOG.md

@@ -3,6 +3,11 @@
 * BREAKING: removed support for ruby < 2.7 and upgraded sexpr
   to 1.1.x
 
+* Added Predicate#assert!, with the help of minitest.
+
+  Implementation is fuly functional, yet error messages will
+  be improved in the future by a better usage of minitest itself.
+
 # 2.7.1 - 2022-04-21
 
 * Add shadow support for Exists tree nodes, that are used by

lib/predicate.rb

@@ -6,6 +6,7 @@
 require_relative 'predicate/grammar'
 require_relative 'predicate/processors'
 require_relative 'predicate/dsl'
+require_relative 'predicate/asserter'
 class Predicate
 
   class Error < StandardError; end
@@ -125,6 +126,10 @@ def call(tuple)
     expr.evaluate(tuple)
   end
 
+  def assert!(tuple = {})
+    expr.assert!(tuple)
+  end
+
   # Splits this predicate, say P, as too predicates P1 & P2
   # such that `P <=> P1 & P2` and P2 makes no reference to
   # any attribute in `attr_list`.

lib/predicate/asserter.rb

@@ -0,0 +1,12 @@
+require 'minitest'
+class Predicate
+  class Asserter
+    include Minitest::Assertions
+
+    def initialize
+      @assertions = 0
+    end
+    attr_accessor :assertions
+
+  end # class Asserter
+end # class Predicate

lib/predicate/nodes/eq.rb

@@ -46,6 +46,12 @@ def evaluate(tuple)
       left.evaluate(tuple) == right.evaluate(tuple)
     end
 
+    def assert!(tuple, asserter = Asserter.new)
+      l, r = left.evaluate(tuple), right.evaluate(tuple)
+      asserter.assert_equal(l, r)
+      l
+    end
+
     def to_hash
       if left.identifier? && right.literal? && !right.has_placeholder?
         { left.name => right.value }

lib/predicate/nodes/expr.rb

@@ -50,6 +50,10 @@ def |(other)
       sexpr([:or, self, other])
     end
 
+    def assert!(tuple, asserter = Asserter.new)
+      asserter.assert(evaluate(tuple))
+    end
+
     def and_split(attr_list)
       # If we have no reference to attr_list, then we are P2, else we are P1
       (free_variables & attr_list).empty? ? [ tautology, self ] : [ self, tautology ]

lib/predicate/nodes/neq.rb

@@ -10,5 +10,11 @@ def evaluate(tuple)
       left.evaluate(tuple) != right.evaluate(tuple)
     end
 
+    def assert!(tuple, asserter = Asserter.new)
+      l, r = left.evaluate(tuple), right.evaluate(tuple)
+      asserter.refute_equal(l, r)
+      l
+    end
+
   end
 end

spec/predicate/test_assert!.rb

@@ -0,0 +1,67 @@
+require 'spec_helper'
+class Predicate
+  describe Predicate, "assert!" do
+
+    describe "eq" do
+      let(:predicate) {
+        Predicate.eq(:x, 2)
+      }
+
+      subject{
+        predicate.assert!(input)
+      }
+
+      context "when ok" do
+        let(:input){
+          { x: 2 }
+        }
+        it 'works and returns 2' do
+          expect(subject).to eql(2)
+        end
+      end
+
+      context "when ko" do
+        let(:input){
+          { x: 3 }
+        }
+        it 'works and throws' do
+          expect{
+            subject
+          }.to raise_error(Minitest::Assertion, /Expected: 3\s+Actual: 2/)
+        end
+      end
+    end
+
+    describe "neq" do
+      let(:predicate) {
+        Predicate.neq(:x, 2)
+      }
+
+      subject{
+        predicate.assert!(input)
+      }
+
+      context "when ok" do
+        let(:input){
+          { x: 3 }
+        }
+        it 'works and returns 3' do
+          expect(subject).to eql(3)
+        end
+      end
+
+      context "when ko" do
+        let(:input){
+          { x: 2 }
+        }
+        it 'works and throws' do
+          expect{
+            subject
+          }.to raise_error(Minitest::Assertion, /Expected 2 to not be equal to 2./)
+        end
+      end
+    end
+
+  end
+end
+