added {length: n} command options + specs

app/js/api/cypress/cy/commands/querying.coffee

@@ -5,6 +5,7 @@ $Cypress.register "Querying", (Cypress, _, $) ->
       _.defaults options,
         retry: true
         withinSubject: @prop("withinSubject")
+        length: null
         visible: null
         exist: true
         exists: true
@@ -114,6 +115,14 @@ $Cypress.register "Querying", (Cypress, _, $) ->
         length = $el.length
 
         switch
+          when options.length isnt null
+            if not _.isFinite(options.length)
+              @throwErr("options.length must be a number")
+
+            if length is options.length
+              log($el)
+              return $el
+
           when options.exist is false
             ## return if we didnt find anything and our options have asked
             ## us for the element not to exist
@@ -145,6 +154,11 @@ $Cypress.register "Querying", (Cypress, _, $) ->
 
       getErr = ->
         err = switch
+          when options.length isnt null
+            if $el.length > options.length
+              "Too many elements found. Found '#{$el.length}', expected '#{options.length}':"
+            else
+              "Not enough elements found. Found '#{$el.length}', expected '#{options.length}':"
           when options.exist is false #and not $el.length
             "Found existing element:"
           when options.visible is false and $el.length

app/js/api/cypress/cy/commands/traversals.coffee

@@ -15,6 +15,7 @@ $Cypress.register "Traversals", (Cypress, _, $) ->
       options ?= {}
 
       _.defaults options,
+        length: null
         visible: null
         exist: true
         exists: true
@@ -63,6 +64,13 @@ $Cypress.register "Traversals", (Cypress, _, $) ->
       length = $el.length
 
       switch
+        when options.length isnt null
+          if not _.isFinite(options.length)
+            @throwErr("options.length must be a number")
+
+          if length is options.length
+            log($el)
+
         when options.exist is false
           ## return if we didnt find anything and our options have asked
           ## us for the element not to exist
@@ -90,6 +98,11 @@ $Cypress.register "Traversals", (Cypress, _, $) ->
 
       getErr = ->
         err = switch
+          when options.length isnt null
+            if $el.length > options.length
+              "Too many elements found. Found '#{$el.length}', expected '#{options.length}':"
+            else
+              "Not enough elements found. Found '#{$el.length}', expected '#{options.length}':"
           when options.exist is false #and not $el.length
             "Found existing element:"
           when options.visible is false and $el.length

spec/client/api/cy/querying_spec.coffee

@@ -313,6 +313,26 @@ describe "$Cypress.Cy Querying Commands", ->
         @cy.get("#button", {visible: true}).then ($button) ->
           expect($button.get(0)).to.eq button.get(0)
 
+    describe "{length: n}", ->
+      it "resolves once length equals n", ->
+        forms = @cy.$("form")
+
+        @cy.get("form", {length: forms.length}).then ($forms) ->
+          expect($forms.length).to.eq forms.length
+
+      it "retries until length equals n", ->
+        buttons = @cy.$("button")
+
+        length = buttons.length - 2
+
+        @cy.on "retry", _.after 2, =>
+          buttons.last().remove()
+          buttons = @cy.$("button")
+
+        ## should resolving after removing 2 buttons
+        @cy.get("button", {length: length}).then ($buttons) ->
+          expect($buttons.length).to.eq length
+
     describe ".log", ->
       beforeEach ->
         @Cypress.on "log", (@log) =>
@@ -548,6 +568,31 @@ describe "$Cypress.Cy Querying Commands", ->
       beforeEach ->
         @allowErrors()
 
+      it "throws when options.length isnt a number", (done) ->
+        @cy.on "fail", (err) ->
+          expect(err.message).to.include "options.length must be a number"
+          done()
+
+        @cy.get("button", {length: "asdf"})
+
+      it "throws on too many elements after timing out waiting for length", (done) ->
+        buttons = @cy.$("button")
+
+        @cy.on "fail", (err) ->
+          expect(err.message).to.include "Too many elements found. Found '#{buttons.length}', expected '#{buttons.length - 1}': button"
+          done()
+
+        @cy.get("button", {length: buttons.length - 1})
+
+      it "throws on too few elements after timing out waiting for length", (done) ->
+        buttons = @cy.$("button")
+
+        @cy.on "fail", (err) ->
+          expect(err.message).to.include "Not enough elements found. Found '#{buttons.length}', expected '#{buttons.length + 1}': button"
+          done()
+
+        @cy.get("button", {length: buttons.length + 1})
+
       it "throws after timing out not finding element", (done) ->
         @cy.get("#missing-el")
 

spec/client/api/cy/traversals_spec.coffee

@@ -25,8 +25,38 @@ describe "$Cypress.Cy Traversal Commands", ->
 
       describe "errors", ->
         beforeEach ->
+          @currentTest.timeout(150)
           @allowErrors()
 
+        it "throws when options.length isnt a number", (done) ->
+          @cy.on "fail", (err) ->
+            expect(err.message).to.include "options.length must be a number"
+            done()
+
+          @cy.get("#list")[name](arg, {length: "asdf"})
+
+        it "throws on too many elements after timing out waiting for length", (done) ->
+          el = @cy.$("#list")[name](arg)
+
+          node = $Cypress.Utils.stringifyElement @cy.$("#list"), "short"
+
+          @cy.on "fail", (err) ->
+            expect(err.message).to.include "Too many elements found. Found '#{el.length}', expected '#{el.length - 1}': #{arg ? ''} from #{node}"
+            done()
+
+          @cy.get("#list")[name](arg, {length: el.length - 1})
+
+        it "throws on too few elements after timing out waiting for length", (done) ->
+          el = @cy.$("#list")[name](arg)
+
+          node = $Cypress.Utils.stringifyElement @cy.$("#list"), "short"
+
+          @cy.on "fail", (err) ->
+            expect(err.message).to.include "Not enough elements found. Found '#{el.length}', expected '#{el.length + 1}': #{arg ? ''} from #{node}"
+            done()
+
+          @cy.get("#list")[name](arg, {length: el.length + 1})
+
         it "without a dom element", (done) ->
           @cy.noop({})[name](arg)
           @cy.on "fail", -> done()
@@ -45,7 +75,7 @@ describe "$Cypress.Cy Traversal Commands", ->
           @cy._timeout(100)
 
           errIncludes = (el, node) =>
-            node = $Cypress.Utils.stringifyElement cy.$(node), "short"
+            node = $Cypress.Utils.stringifyElement @cy.$(node), "short"
 
             @cy.on "fail", (err) ->
               expect(err.message).to.include "Could not find element: #{el} from #{node}"