Expectation class

functions/postwomanTesting.js

@@ -1,6 +1,7 @@
 export default function runTestScriptWitVariables(script, variables) {
 
   let pw = {
+    _errors: [],
     assert
     // globals that the script is allowed to have access to.
   };
@@ -24,6 +25,58 @@ function assert(expression) {
   }
 }
 
+function expect(expectValue) {
+  return new Expectation(expectValue);
+}
+
+class Expectation {
+  constructor(expectValue, _not, _testReports) {
+    this.expectValue = expectValue;
+    this.not = _not || new Expectation(this.expectValue, true);
+    this._testReports = _testReports; // this values is used within Test.it, which wraps Expectation and passes _testReports value.
+    this._satisfies = function(targetValue) {
+      // Used for testing if two values match the expectation, which could be === OR !==, depending on if not
+      // was used. Expectation#_satisfies prevents the need to have an if(this.not) branch in every test method.
+      if (this.not === true) {
+        // test the inverse. this.not is always truthly, but an Expectation that is inverted will always be strictly `true`
+        return this.expectValue !== targetValue;
+      } else {
+        return this.expectValue === targetValue;
+      }
+    }
+  }
+  _fmtNot(message) {
+    // given a string with "(not)" in it, replaces with "not" or "", depending if the expectation is expecting the positive or inverse (this._not)
+    if (this.not === true) {
+      return message.replace("(not)", "not ");
+    } else {
+      return message.replace("(not)", "")
+    }
+  }
+  _fail(message) {
+    if (this._testReports) {
+      this._testReports.push({pass: false, message})
+    } else {
+      throw {message}
+    }
+  }
+  _pass(message) {
+    if (this._testReports) {
+      this._testReports.push({pass: true, message});
+    } else {
+      return true;
+    }
+  }
+  // TEST METHODS DEFINED BELOW
+  // these are the usual methods that would follow expect(...)
+  toBe(value) {
+    return this._satisfies(value) ? this._pass() : this._fail(this._fmtNot(`Expected ${this.expectValue} (not)to be ${value}`));
+  }
+  toHaveProperty(value) {
+    return this._satisfies(this.expectValue.hasOwnProperty(value)) ? this._pass() : this._fail(`Expected object ${this.expectValue} to (not)have property ${value}`)
+  }
+}
+
 class PostwomanTestFailure {
   constructor(message) {
     return {message}