test: introduces custom chai assertions

.eslintrc.js

@@ -12,6 +12,10 @@ module.exports = {
     'no-plusplus': 'off',
     'func-names': 'off',
 
+    // Disabled to allow "expect()" assertions with parameters:
+    // expect(foo).to.be.valid
+    'no-unused-expressions': 'off',
+
     // Temporary overrides. Logic to be rewritten.
     // TODO https://github.com/apiaryio/gavel.js/issues/150
     'no-param-reassign': 'off'

test/chai.js

@@ -0,0 +1,107 @@
+/* eslint-disable no-underscore-dangle */
+const chai = require('chai');
+
+const stringify = (obj) => {
+  return JSON.stringify(obj, null, 2);
+};
+
+chai.use(({ Assertion }, utils) => {
+  utils.addProperty(Assertion.prototype, 'valid', function() {
+    const { isValid } = this._obj;
+    const stringifiedObj = stringify(this._obj);
+
+    this.assert(
+      isValid === true,
+      `
+Expected the following HTTP message field:
+
+${stringifiedObj}
+
+to have "isValid" equal #{exp}, but got #{act}'.
+`,
+      `
+Expected the following HTTP message field:
+
+${stringifiedObj}
+
+to be invalid, but it is actually valid.`
+    );
+  });
+
+  Assertion.addMethod('validator', function(expectedValue) {
+    const { validator: actualValue } = this._obj;
+    const stringifiedObj = stringify(this._obj);
+
+    this.assert(
+      actualValue === expectedValue,
+      `
+Expected the following HTTP message field:
+
+${stringifiedObj}
+
+to have "${expectedValue}" validator, but got "${actualValue}".
+      `,
+      `
+Expected the following HTTP message field:
+
+${stringifiedObj}
+
+to not have validator equal to "${expectedValue}".
+`,
+      expectedValue,
+      actualValue
+    );
+  });
+
+  Assertion.addMethod('expectedType', function(expectedValue) {
+    const { expectedType: actualValue } = this._obj;
+    const stringifiedObj = stringify(this._obj);
+
+    this.assert(
+      actualValue === expectedValue,
+      `
+Expected the following HTTP message field:
+
+${stringifiedObj}
+
+to have an "expectedType" equal to "${expectedValue}", but got "${actualValue}".
+  `,
+      `
+Expected the following HTTP message field:
+
+${stringifiedObj}
+
+to not have an "expectedType" of "${expectedValue}".
+      `,
+      expectedValue,
+      actualValue
+    );
+  });
+
+  Assertion.addMethod('realType', function(expectedValue) {
+    const { realType: actualValue } = this._obj;
+    const stringifiedObj = stringify(this._obj);
+
+    this.assert(
+      actualValue === expectedValue,
+      `
+Expected the following HTTP message field:
+
+${stringifiedObj}
+
+to have an "realType" equal to "${expectedValue}", but got "${actualValue}".
+`,
+      `
+Expected the following HTTP message field:
+
+${stringifiedObj}
+
+to not have an "realType" of "${expectedValue}".
+      `,
+      expectedValue,
+      actualValue
+    );
+  });
+});
+
+module.exports = chai;