mungedb-aggregate/test/lib/pipeline/expressions/ObjectExpression.js

"use strict";
var assert = require("assert"),
	ObjectExpression = require("../../../../lib/pipeline/expressions/ObjectExpression"),
	ConstantExpression = require("../../../../lib/pipeline/expressions/ConstantExpression"),
	FieldPathExpression = require("../../../../lib/pipeline/expressions/FieldPathExpression"),
	AndExpression = require("../../../../lib/pipeline/expressions/AndExpression"),
	Variables = require("../../../../lib/pipeline/expressions/Variables");


function assertEqualJson(actual, expected, message){
	if(actual.sort) {
		actual.sort();
		if(expected.sort) {
			expected.sort();
		}
	}
	assert.strictEqual(message + ":  " + JSON.stringify(actual), message + ":  " + JSON.stringify(expected));
}

/// An assertion for `ObjectExpression` instances based on Mongo's `ExpectedResultBase` class
function assertExpectedResult(args) {
	{// check for required args
		if (args === undefined) throw new TypeError("missing arg: `args` is required");
		if (!("expected" in args)) throw new Error("missing arg: `args.expected` is required");
		if (!("expectedDependencies" in args)) throw new Error("missing arg: `args.expectedDependencies` is required");
		if (!("expectedJsonRepresentation" in args)) throw new Error("missing arg: `args.expectedJsonRepresentation` is required");
	}// check for required args
	{// base args if none provided
		if (args.source === undefined) args.source = {_id:0, a:1, b:2};
		if (args.expectedIsSimple === undefined) args.expectedIsSimple = false;
		if (args.expression === undefined) args.expression = ObjectExpression.createRoot(); //NOTE: replaces prepareExpression + _expression assignment
	}// base args if none provided
	// run implementation
	var result = {},
		variable = new Variables(1, args.source);

	args.expression.addToDocument(result, args.source, variable);
	assert.deepEqual(result, args.expected);
	var dependencies = {};
	args.expression.addDependencies(dependencies, [/*FAKING: includePath=true*/]);
	//dependencies.sort(), args.expectedDependencies.sort();	// NOTE: this is a minor hack added for munge because I'm pretty sure order doesn't matter for this anyhow
	assert.deepEqual(Object.keys(dependencies).sort(), Object.keys(args.expectedDependencies).sort());
	assert.deepEqual(args.expression.serialize(true), args.expectedJsonRepresentation);
	assert.deepEqual(args.expression.getIsSimple(), args.expectedIsSimple);
}


module.exports = {

	"ObjectExpression": {

		"constructor()": {

			"should not throw Error when constructing without args": function testConstructor(){
				assert.doesNotThrow(function(){
					ObjectExpression.create();
				});
			}

		},

		"#addDependencies":{

			"should be able to get dependencies for non-inclusion expressions": function testNonInclusionDependencies(){
				/** Dependencies for non inclusion expressions. */
				var expr = ObjectExpression.create();
				expr.addField("a", new ConstantExpression(5));
				var depsTracker = {fields:{}};
				assertEqualJson(expr.addDependencies(depsTracker, [/*FAKING: includePath=true*/]), {fields:{"_id":1}}, "Message");
				expr.excludeId = true;
				assertEqualJson(expr.addDependencies(depsTracker, []), {fields:{"_id":1}});
				expr.addField("b", FieldPathExpression.create("c.d"));
				//var deps = {};
				depsTracker = {fields:{}};
				expr.addDependencies(depsTracker, []);
				assert.deepEqual(depsTracker, {fields:{"c.d":1}});
				expr.excludeId = false;
				//deps = {};
				depsTracker = {fields:{}}
				expr.addDependencies(depsTracker, []);
				assert.deepEqual(depsTracker, {fields:{"_id":1,"c.d":1}});
			},

			"should be able to get dependencies for inclusion expressions": function testInclusionDependencies(){
				/** Dependencies for inclusion expressions. */
				var expr = ObjectExpression.create();
				expr.includePath( "a" );
				var depsTracker = {fields:{}};
				assertEqualJson(expr.addDependencies(depsTracker, [/*FAKING: includePath=true*/]), {"fields":{"_id":1,"a":1}});
				assert.throws(function(){
					expr.addDependencies({});
				}, Error);
			}

		},

		"#toJSON": {

			"should be able to convert to JSON representation and have constants represented by expressions": function testJson(){
				/** Serialize to a BSONObj, with constants represented by expressions. */
				var expr = ObjectExpression.create(true);
				expr.addField("foo.a", new ConstantExpression(5));
				assertEqualJson({foo:{a:{$const:5}}}, expr.serialize(true));
			}

		},

		"#optimize": {

			"should be able to optimize expression and sub-expressions": function testOptimize(){
				/** Optimizing an object expression optimizes its sub expressions. */
				var expr = ObjectExpression.createRoot();
				// Add inclusion.
				expr.includePath( "a" );
				// Add non inclusion.
				expr.addField( "b", new AndExpression());
				expr.optimize();
				// Optimizing 'expression' optimizes its non inclusion sub expressions, while inclusion sub expressions are passed through.
				assertEqualJson({a:{$const:null}, b:{$const:true}}, expr.serialize(true));
			}

		},

		"#evaluate()": {

			"should be able to provide an empty object": function testEmpty(){
				/** Empty object spec. */
				var expr = ObjectExpression.createRoot();
				assertExpectedResult({
					expression: expr,
					expected: {"_id":0},
					expectedDependencies: {"fields":1},
					expectedJsonRepresentation: {}
				});
			},

			"should be able to include 'a' field only": function testInclude(){
				/** Include 'a' field only. */
				var expr = ObjectExpression.createRoot();
				expr.includePath( "a" );
				assertExpectedResult({
					expression: expr,
					expected: {"_id":0, "a":1},
					expectedDependencies: {"_id":1, "a":1},
					expectedJsonRepresentation: {"a":{$const:null}}
				});
			},

			"should NOT be able to include missing 'a' field": function testMissingInclude(){
				/** Cannot include missing 'a' field. */
				var expr = ObjectExpression.createRoot();
				expr.includePath( "a" );
				assertExpectedResult({
					source: {"_id":0, "b":2},
					expression: expr,
					expected: {"_id":0},
					expectedDependencies: {"_id":1, "a":1},
					expectedJsonRepresentation: {"a":{$const:null}}
				});
			},

			"should be able to include '_id' field only": function testIncludeId(){
				/** Include '_id' field only. */
				var expr = ObjectExpression.createRoot();
				expr.includePath( "_id" );
				assertExpectedResult({
					expression: expr,
					expected: {"_id":0},
					expectedDependencies: {"_id":1},
					expectedJsonRepresentation: {"_id":{$const:null}}
				});
			},

			"should be able to exclude '_id' field": function testExcludeId(){
				/** Exclude '_id' field. */
				var expr = ObjectExpression.createRoot();
				expr.includePath( "b" );
				expr.excludeId = true;
				assertExpectedResult({
					expression: expr,
					expected: {"b":2},
					expectedDependencies: {"b":1},
					expectedJsonRepresentation: {"b":{$const:null}}
				});
			},

			"should be able to include fields in source document order regardless of inclusion order": function testSourceOrder(){
				/** Result order based on source document field order, not inclusion spec field order. */
				var expr = ObjectExpression.createRoot();
				expr.includePath( "b" );
				expr.includePath( "a" );
				assertExpectedResult({
					expression: expr,
					get expected() { return this.source; },
					expectedDependencies: {"_id":1, "a":1, "b":1},
					expectedJsonRepresentation: {"b":{$const:null}, "a":{$const:null}}
				});
			},

			"should be able to include a nested field": function testIncludeNested(){
				/** Include a nested field. */
				var expr = ObjectExpression.createRoot();
				expr.includePath( "a.b" );
				assertExpectedResult({
					source: {"_id":0, "a":{ "b":5, "c":6}, "z":2 },
					expression: expr,
					expected: {"_id":0, "a":{ "b":5} },
					expectedDependencies: {"_id":1, "a.b":1},
					expectedJsonRepresentation: {"a":{ "b":{$const:null}} }
				});
			},

			"should be able to include two nested fields": function testIncludeTwoNested(){
				/** Include two nested fields. */
				var expr = ObjectExpression.createRoot();
				expr.includePath( "a.b" );
				expr.includePath( "a.c" );
				assertExpectedResult({
					source: {"_id":0, "a":{ "b":5, "c":6}, "z":2 },
					expression: expr,
					expected: {"_id":0, "a":{ "b":5, "c":6} },
					expectedDependencies: {"_id":1, "a.b":1, "a.c":1},
					expectedJsonRepresentation: {"a":{ "b":{$const:null}, "c":{$const:null}} }
				});
			},

			"should be able to include two fields nested within different parents": function testIncludeTwoParentNested(){
				/** Include two fields nested within different parents. */
				var expr = ObjectExpression.createRoot();
				expr.includePath( "a.b" );
				expr.includePath( "c.d" );
				assertExpectedResult({
					source: {"_id":0, "a":{ "b":5 }, "c":{"d":6} },
					expression: expr,
					expected: {"_id":0, "a":{ "b":5}, "c":{"d":6} },
					expectedDependencies: {"_id":1, "a.b":1, "c.d":1},
					expectedJsonRepresentation: {"a":{"b":{$const:null}}, "c":{"d":{$const:null}} }
				});
			},

			"should be able to attempt to include a missing nested field": function testIncludeMissingNested(){
				/** Attempt to include a missing nested field. */
				var expr = ObjectExpression.createRoot();
				expr.includePath( "a.b" );
				assertExpectedResult({
					source: {"_id":0, "a":{ "c":6}, "z":2 },
					expression: expr,
					expected: {"_id":0, "a":{} },
					expectedDependencies: {"_id":1, "a.b":1},
					expectedJsonRepresentation: {"a":{ "b":{$const:null}} }
				});
			},

			"should be able to attempt to include a nested field within a non object": function testIncludeNestedWithinNonObject(){
				/** Attempt to include a nested field within a non object. */
				var expr = ObjectExpression.createRoot();
				expr.includePath( "a.b" );
				assertExpectedResult({
					source: {"_id":0, "a":2, "z":2},
					expression: expr,
					expected: {"_id":0},
					expectedDependencies: {"_id":1, "a.b":1},
					expectedJsonRepresentation: {"a":{ "b":{$const:null}} }
				});
			},

			"should be able to include a nested field within an array": function testIncludeArrayNested(){
				/** Include a nested field within an array. */
				var expr = ObjectExpression.createRoot();
				expr.includePath( "a.b" );
				assertExpectedResult({
					source: {_id:0,a:[{b:5,c:6},{b:2,c:9},{c:7},[],2],z:1},
					expression: expr,
					expected: {_id:0,a:[{b:5},{b:2},{}]},
					expectedDependencies: {"_id":1, "a.b":1},
					expectedJsonRepresentation: {"a":{ "b":{$const:null}} }
				});
			},

			"should NOT include non-root '_id' field implicitly": function testExcludeNonRootId(){
				/** Don't include not root '_id' field implicitly. */
				var expr = ObjectExpression.createRoot();
				expr.includePath( "a.b" );
				assertExpectedResult({
					source: {"_id":0, "a":{ "_id":1, "b":1} },
					expression: expr,
					expected: {"_id":0, "a":{ "b":1} },
					expectedDependencies: {"_id":1, "a.b":1},
					expectedJsonRepresentation: {"a":{ "b":{$const:null}}}
				});
			},

			"should be able to project a computed expression": function testComputed(){
				/** Project a computed expression. */
				var expr = ObjectExpression.createRoot();
				expr.addField("a", new ConstantExpression(5));
				assertExpectedResult({
					source: {"_id":0},
					expression: expr,
					expected: {"_id":0, "a":5},
					expectedDependencies: {"_id":1},
					expectedJsonRepresentation: {"a":{ "$const":5} },
					expectedIsSimple: false
				});
			},

			"should be able to project a computed expression replacing an existing field": function testComputedReplacement(){
				/** Project a computed expression replacing an existing field. */
				var expr = ObjectExpression.createRoot();
				expr.addField("a", new ConstantExpression(5));
				assertExpectedResult({
					source: {"_id":0, "a":99},
					expression: expr,
					expected: {"_id": 0, "a": 5},
					expectedDependencies: {"_id":1},
					expectedJsonRepresentation: {"a": {"$const": 5}},
					expectedIsSimple: false
				});
			},

			"should NOT be able to project an undefined value": function testComputedUndefined(){
				/** An undefined value is not projected.. */
				var expr = ObjectExpression.createRoot();
				expr.addField("a", new ConstantExpression(undefined));
				assertExpectedResult({
					source: {"_id":0},
					expression: expr,
					expected: {"_id":0},
					expectedDependencies: {"_id":1},
					expectedJsonRepresentation: {a:{$const:undefined}},
					expectedIsSimple: false
				});
			},

			"should be able to project a computed expression replacing an existing field with Undefined": function testComputedUndefinedReplacement(){
				/** Project a computed expression replacing an existing field with Undefined. */
				var expr = ObjectExpression.createRoot();
				expr.addField("a", new ConstantExpression(5));
				assertExpectedResult({
					source: {"_id":0, "a":99},
					expression: expr,
					expected: {"_id":0, "a":5},
					expectedDependencies: {"_id":1},
					expectedJsonRepresentation: {"a":{"$const":5}},
					expectedIsSimple: false
				});
			},

			"should be able to project a null value": function testComputedNull(){
				/** A null value is projected. */
				var expr = ObjectExpression.createRoot();
				expr.addField("a", new ConstantExpression(null));
				assertExpectedResult({
					source: {"_id":0},
					expression: expr,
					expected: {"_id":0, "a":null},
					expectedDependencies: {"_id":1},
					expectedJsonRepresentation: {"a":{"$const":null}},
					expectedIsSimple: false
				});
			},

			"should be able to project a nested value": function testComputedNested(){
				/** A nested value is projected. */
				var expr = ObjectExpression.createRoot();
				expr.addField("a.b", new ConstantExpression(5));
				assertExpectedResult({
					source: {"_id":0},
					expression: expr,
					expected: {"_id":0, "a":{"b":5}},
					expectedDependencies: {"_id":1},
					expectedJsonRepresentation: {"a":{"b":{"$const":5}}},
					expectedIsSimple: false
				});
			},

			"should be able to project a field path": function testComputedFieldPath(){
				/** A field path is projected. */
				var expr = ObjectExpression.createRoot();
				expr.addField("a", FieldPathExpression.create("x"));
				assertExpectedResult({
					source: {"_id":0, "x":4},
					expression: expr,
					expected: {"_id":0, "a":4},
					expectedDependencies: {"_id":1, "x":1},
					expectedJsonRepresentation: {"a":"$x"},
					expectedIsSimple: false
				});
			},

			"should be able to project a nested field path": function testComputedNestedFieldPath(){
				/** A nested field path is projected. */
				var expr = ObjectExpression.createRoot();
				expr.addField("a.b", FieldPathExpression.create("x.y"));
				assertExpectedResult({
					source: {"_id":0, "x":{"y":4}},
					expression: expr,
					expected: {"_id":0, "a":{"b":4}},
					expectedDependencies: {"_id":1, "x.y":1},
					expectedJsonRepresentation: {"a":{"b":"$x.y"}},
					expectedIsSimple: false
				});
			},

			"should NOT project an empty subobject expression for a missing field": function testEmptyNewSubobject(){
				/** An empty subobject expression for a missing field is not projected. */
				var expr = ObjectExpression.createRoot();
				// Create a sub expression returning an empty object.
				var subExpr = ObjectExpression.create();
				subExpr.addField("b", FieldPathExpression.create("a.b"));
				expr.addField( "a", subExpr );
				assertExpectedResult({
					source: {"_id":0},
					expression: expr,
					expected: {"_id":0},
					expectedDependencies: {"_id":1, 'a.b':1},
					expectedJsonRepresentation: {a:{b:"$a.b"}},
					expectedIsSimple: false
				});
			},

			"should be able to project a non-empty new subobject": function testNonEmptyNewSubobject(){
				/** A non empty subobject expression for a missing field is projected. */
				var expr = ObjectExpression.createRoot();
				// Create a sub expression returning an empty object.
				var subExpr = ObjectExpression.create();
				subExpr.addField("b", new ConstantExpression(6));
				expr.addField( "a", subExpr );
				assertExpectedResult({
					source: {"_id":0},
					expression: expr,
					expected: {"_id":0, "a":{ "b":6} },
					expectedDependencies: {"_id":1},
					expectedJsonRepresentation: {a:{b:{$const:6}}},
					expectedIsSimple: false
				});
			},

			"should be able to project two computed fields within a common parent": function testAdjacentDottedComputedFields(){
				/** Two computed fields within a common parent. */
				var expr = ObjectExpression.createRoot();
				expr.addField("a.b", new ConstantExpression(6));
				expr.addField("a.c", new ConstantExpression(7));
				assertExpectedResult({
					source: {"_id":0},
					expression: expr,
					expected: {"_id":0, "a":{ "b":6, "c":7} },
					expectedDependencies: {"_id":1},
					expectedJsonRepresentation: {a:{b:{$const:6},c:{$const:7}}},
					expectedIsSimple: false
				});
			},

			"should be able to project two computed fields within a common parent (w/ one case dotted)": function testAdjacentDottedAndNestedComputedFields(){
				/** Two computed fields within a common parent, in one case dotted. */
				var expr = ObjectExpression.createRoot();
				expr.addField("a.b", new ConstantExpression(6));
				var subExpr = ObjectExpression.create();
				subExpr.addField("c", new ConstantExpression( 7 ) );
				expr.addField("a", subExpr);
				assertExpectedResult({
					source: {"_id":0},
					expression: expr,
					expected: {"_id":0, "a":{ "b":6, "c":7} },
					expectedDependencies: {"_id":1},
					expectedJsonRepresentation: {a:{b:{$const:6},c:{$const:7}}},
					expectedIsSimple: false
				});
			},

			"should be able to project two computed fields within a common parent (in another case dotted)": function testAdjacentNestedAndDottedComputedFields(){
				/** Two computed fields within a common parent, in another case dotted. */
				var expr = ObjectExpression.createRoot();
				var subExpr = ObjectExpression.create();
				subExpr.addField("b", new ConstantExpression(6));
				expr.addField("a", subExpr );
				expr.addField("a.c", new ConstantExpression(7));
				assertExpectedResult({
					source: {"_id":0},
					expression: expr,
					expected: {"_id":0, "a":{ "b":6, "c":7} },
					expectedDependencies: {"_id":1},
					expectedJsonRepresentation: {a:{b:{$const:6},c:{$const:7}}},
					expectedIsSimple: false
				});
			},

			"should be able to project two computed fields within a common parent (nested rather than dotted)": function testAdjacentNestedComputedFields(){
				/** Two computed fields within a common parent, nested rather than dotted. */
				var expr = ObjectExpression.createRoot();
				var subExpr1 = ObjectExpression.create();
				subExpr1.addField("b", new ConstantExpression(6));
				expr.addField("a", subExpr1);
				var subExpr2 = ObjectExpression.create();
				subExpr2.addField("c", new ConstantExpression(7));
				expr.addField("a", subExpr2);
				assertExpectedResult({
					source: {"_id":0},
					expression: expr,
					expected: {"_id":0, "a":{ "b":6, "c":7} },
					expectedDependencies: {"_id":1},
					expectedJsonRepresentation: {a:{b:{$const:6},c:{$const:7}}},
					expectedIsSimple: false
				});
			},

			"should be able to project multiple nested fields out of order without affecting output order": function testAdjacentNestedOrdering(){
				/** Field ordering is preserved when nested fields are merged. */
				var expr = ObjectExpression.createRoot();
				expr.addField("a.b", new ConstantExpression(6));
				var subExpr = ObjectExpression.create();
				// Add field 'd' then 'c'.  Expect the same field ordering in the result doc.
				subExpr.addField("d", new ConstantExpression(7));
				subExpr.addField("c", new ConstantExpression(8));
				expr.addField("a", subExpr);
				assertExpectedResult({
					source: {"_id":0},
					expression: expr,
					expected: {"_id":0, "a":{ "b":6, "d":7, "c":8} },
					expectedDependencies: {"_id":1},
					expectedJsonRepresentation: {a:{b:{$const:6},d:{$const:7},c:{$const:8}}},
					expectedIsSimple: false
				});
			},

			"should be able to project adjacent fields two levels deep": function testMultipleNestedFields(){
				/** Adjacent fields two levels deep. */
				var expr = ObjectExpression.createRoot();
				expr.addField("a.b.c", new ConstantExpression(6));
				var bSubExpression = ObjectExpression.create();
				bSubExpression.addField("d", new ConstantExpression(7));
				var aSubExpression = ObjectExpression.create();
				aSubExpression.addField("b", bSubExpression);
				expr.addField("a", aSubExpression);
				assertExpectedResult({
					source:{_id:0},
					expression: expr,
					expected: {"_id":0, "a":{ "b":{ "c":6, "d":7}}},
					expectedDependencies:{_id:1},
					expectedJsonRepresentation:{"a":{"b":{"c":{$const:6},"d":{$const:7}}}},
					expectedIsSimple:false
				});
				var res = expr.evaluateDocument(new Variables(1, {_id:1}));
			},

			"should throw an Error if two expressions generate the same field": function testConflictingExpressionFields(){
				/** Two expressions cannot generate the same field. */
				var expr = ObjectExpression.createRoot();
				expr.addField("a", new ConstantExpression(5));
				assert.throws(function(){
					expr.addField("a", new ConstantExpression(6)); // Duplicate field.
				}, Error);
			},

			"should throw an Error if an expression field conflicts with an inclusion field": function testConflictingInclusionExpressionFields(){
				/** An expression field conflicts with an inclusion field. */
				var expr = ObjectExpression.createRoot();
				expr.includePath("a");
				assert.throws(function(){
					expr.addField("a", new ConstantExpression(6));
				}, Error);
			},

			"should throw an Error if an inclusion field conflicts with an expression field": function testConflictingExpressionInclusionFields(){
				/** An inclusion field conflicts with an expression field. */
				var expr = ObjectExpression.createRoot();
				expr.addField("a", new ConstantExpression(5));
				assert.throws(function(){
					expr.includePath("a");
				}, Error);
			},

			"should throw an Error if an object expression conflicts with a constant expression": function testConflictingObjectConstantExpressionFields(){
				/** An object expression conflicts with a constant expression. */
				var expr = ObjectExpression.createRoot();
				var subExpr = ObjectExpression.create();
				subExpr.includePath("b");
				expr.addField("a", subExpr);
				assert.throws(function(){
					expr.addField("a.b", new ConstantExpression(6));
				}, Error);
			},

			"should throw an Error if a constant expression conflicts with an object expression": function testConflictingConstantObjectExpressionFields(){
				/** A constant expression conflicts with an object expression. */
				var expr = ObjectExpression.createRoot();
				expr.addField("a.b", new ConstantExpression(6));
				var subExpr = ObjectExpression.create();
				subExpr.includePath("b");
				assert.throws(function(){
					expr.addField("a", subExpr);
				}, Error);
			},

			"should throw an Error if two nested expressions cannot generate the same field": function testConflictingNestedFields(){
				/** Two nested expressions cannot generate the same field. */
				var expr = ObjectExpression.createRoot();
				expr.addField("a.b", new ConstantExpression(5));
				assert.throws(function(){
					expr.addField("a.b", new ConstantExpression(6));	// Duplicate field.
				}, Error);
			},

			"should throw an Error if an expression is created for a subfield of another expression": function testConflictingFieldAndSubfield(){
				/** An expression cannot be created for a subfield of another expression. */
				var expr = ObjectExpression.createRoot();
				expr.addField("a", new ConstantExpression(5));
				assert.throws(function(){
					expr.addField("a.b", new ConstantExpression(5));
				}, Error);
			},

			"should throw an Error if an expression is created for a nested field of another expression.": function testConflictingFieldAndNestedField(){
				/** An expression cannot be created for a nested field of another expression. */
				var expr = ObjectExpression.createRoot();
				expr.addField("a", new ConstantExpression(5));
				var subExpr = ObjectExpression.create();
				subExpr.addField("b", new ConstantExpression(5));
				assert.throws(function(){
					expr.addField("a", subExpr);
				}, Error);
			},

			"should throw an Error if an expression is created for a parent field of another expression": function testConflictingSubfieldAndField(){
				/** An expression cannot be created for a parent field of another expression. */
				var expr = ObjectExpression.createRoot();
				expr.addField("a.b", new ConstantExpression(5));
				assert.throws(function(){
					expr.addField("a", new ConstantExpression(5));
				}, Error);
			},

			"should throw an Error if an expression is created for a parent of a nested field": function testConflictingNestedFieldAndField(){
				/** An expression cannot be created for a parent of a nested field. */
				var expr = ObjectExpression.createRoot();
				var subExpr = ObjectExpression.create();
				subExpr.addField("b", new ConstantExpression(5));
				expr.addField("a", subExpr);
				assert.throws(function(){
					expr.addField("a", new ConstantExpression(5));
				}, Error);
			},

			"should be able to evaluate expressions in general": function testEvaluate(){
				/**
				 * evaluate() does not supply an inclusion document.
				 * Inclusion spec'd fields are not included.
				 * (Inclusion specs are not generally expected/allowed in cases where evaluate is called instead of addToDocument.)
				 */
				var expr = ObjectExpression.createRoot();
				expr.includePath("a");
				expr.addField("b", new ConstantExpression(5));
				expr.addField("c", FieldPathExpression.create("a"));
				var res = expr.evaluateInternal(new Variables(1, {_id:0, a:1}));
				assert.deepEqual({"b":5, "c":1}, res);
			}
		}

	}

};

if (!module.parent)(new(require("mocha"))()).ui("exports").reporter("spec").addFile(__filename).run(process.exit);