diff --git a/lib/ex_unit/lib/ex_unit/assertions.ex b/lib/ex_unit/lib/ex_unit/assertions.ex
index 26abca98ad..2eaf44abd0 100644
--- a/lib/ex_unit/lib/ex_unit/assertions.ex
+++ b/lib/ex_unit/lib/ex_unit/assertions.ex
@@ -266,7 +266,7 @@ defmodule ExUnit.Assertions do
         if name == ExUnit.AssertionError do
           raise(error)
         else
-          flunk "Expected exception #{inspect exception}, got #{inspect name}"
+          flunk "Expected exception #{inspect exception}, got #{inspect name} (#{error.message})"
         end
     end
   end
diff --git a/lib/ex_unit/test/ex_unit/assertions_test.exs b/lib/ex_unit/test/ex_unit/assertions_test.exs
index 3b4a7e7779..3012b39938 100644
--- a/lib/ex_unit/test/ex_unit/assertions_test.exs
+++ b/lib/ex_unit/test/ex_unit/assertions_test.exs
@@ -188,7 +188,7 @@ defmodule ExUnit.AssertionsTest do
       end
     rescue
       error in [ExUnit.AssertionError] ->
-        "Expected exception ArgumentError, got UndefinedFunctionError" = error.message
+        "Expected exception ArgumentError, got UndefinedFunctionError (undefined function: Certainly.Undefined.function/3)" = error.message
     end
   end
 
@@ -199,7 +199,7 @@ defmodule ExUnit.AssertionsTest do
       end
     rescue
       error in [ExUnit.AssertionError] ->
-        "Expected exception SyntaxError, got FunctionClauseError" = error.message
+        "Expected exception SyntaxError, got FunctionClauseError (no function clause matching: :lists.flatten(1))" = error.message
     end
   end
 
diff --git a/lib/mix/lib/mix/cli.ex b/lib/mix/lib/mix/cli.ex
index 042ca11552..be66f7f673 100644
--- a/lib/mix/lib/mix/cli.ex
+++ b/lib/mix/lib/mix/cli.ex
@@ -2,7 +2,7 @@ defmodule Mix.CLI do
   @moduledoc false
 
   defmacrop exceptions do
-    [Mix.Error, Mix.NoTaskError, Mix.InvalidTaskError, Mix.NoProjectError]
+    [Mix.Error, Mix.NoTaskError, Mix.InvalidTaskError, Mix.NoProjectError, Mix.NotMetDepsError]
   end
 
   @doc """
diff --git a/lib/mix/lib/mix/exceptions.ex b/lib/mix/lib/mix/exceptions.ex
index 45f9424e68..7c52d98812 100644
--- a/lib/mix/lib/mix/exceptions.ex
+++ b/lib/mix/lib/mix/exceptions.ex
@@ -12,4 +12,6 @@ end
 
 defexception Mix.NoProjectError, message: "Could not find a Mix.Project"
 
-defexception Mix.Error, message: nil
\ No newline at end of file
+defexception Mix.Error, message: nil
+
+defexception Mix.NotMetDepsError, message: "Some dependencies were not met"
\ No newline at end of file
diff --git a/lib/mix/lib/mix/scm/git.ex b/lib/mix/lib/mix/scm/git.ex
index 36e61f02c8..4c5ff57de7 100644
--- a/lib/mix/lib/mix/scm/git.ex
+++ b/lib/mix/lib/mix/scm/git.ex
@@ -1,5 +1,5 @@
 defmodule Mix.SCM.Git do
-  def cloned?(path) do
+  def available?(path) do
     File.dir?(File.join(path, ".git"))
   end
 end
\ No newline at end of file
diff --git a/lib/mix/lib/mix/tasks/deps.check.ex b/lib/mix/lib/mix/tasks/deps.check.ex
new file mode 100644
index 0000000000..acc1f64635
--- /dev/null
+++ b/lib/mix/lib/mix/tasks/deps.check.ex
@@ -0,0 +1,32 @@
+defmodule Mix.Tasks.Deps.Check do
+  use Mix.Task
+
+  import Mix.Tasks.Deps, [all: 0, format_dep: 1, format_status: 1]
+
+  @moduledoc """
+  Checks if all dependencies are valid and if not, abort.
+  Prints the invalid dependencies status before aborting.
+
+  This task is not exhibited in `mix help` but it is part
+  of mix public API and can be depended on.
+  """
+  def run(_) do
+    case Enum.partition all, match?({ _, _, _, { :ok, _ }, _ }, &1) do
+      { _, [] }     -> :ok
+      { _, not_ok } ->
+        if Enum.all? not_ok, match?({ _, _, _, { :unavailable, _ }, _ }, &1) do
+          raise Mix.NotMetDepsError, message:
+            "Dependencies are not available, run `mix deps.get` before proceeding"
+        else
+          shell = Mix.shell
+
+          Enum.each not_ok, fn(dep) ->
+            shell.error "* #{format_dep(dep)}"
+            shell.error "  #{format_status elem(dep, 4)}"
+          end
+
+          raise Mix.NotMetDepsError
+        end
+    end
+  end
+end
diff --git a/lib/mix/lib/mix/tasks/deps.ex b/lib/mix/lib/mix/tasks/deps.ex
index 411f8fb0cd..7d9ef4ecf9 100644
--- a/lib/mix/lib/mix/tasks/deps.ex
+++ b/lib/mix/lib/mix/tasks/deps.ex
@@ -3,6 +3,10 @@ defmodule Mix.Tasks.Deps do
 
   @shortdoc "List dependencies and their status"
 
+  @moduledoc """
+  List all dependencies and their status.
+  """
+
   @doc """
   Returns all dependencies in the following format:
 
@@ -24,18 +28,25 @@ defmodule Mix.Tasks.Deps do
     Enum.map deps, with_scm_and_status(&1)
   end
 
+  @doc """
+  Get all dependencies that match the specific `status`.
+  """
+  def all(status) do
+    Enum.filter all, match?({ _, _, _, { ^status, _ }, _ }, &1)
+  end
+
   @doc """
   Formats the status of a dependency. It can be either:
 
   * `{ :ok, vsn }` - Everything is :ok, got version `vsn`;
-  * `{ :uncloned, path }` - The dependency is not checked out;
+  * `{ :unavailable, path }` - The dependency is not available;
   * `{ :noappfile, path }` - The .app file at path could not be found;
   * `{ :invalidapp, path }` - The .app file at path is not properly formatted;
   * `{ :invalidvsn, actual }` - The dependency does not match the specified requirement, got `actual`;
 
   """
   def format_status({ :ok, _vsn }),         do: "ok"
-  def format_status({ :uncloned, path }),   do: "the dependency is not checked out at: #{path}"
+  def format_status({ :unavailable, _ }),   do: "the dependency is not available, run `mix deps.get`"
   def format_status({ :noappfile, path }),  do: "could not find app file at #{path}"
   def format_status({ :invalidapp, path }), do: "the app file at #{path} is invalid"
   def format_status({ :invalidvsn, vsn }),  do: "the dependency does not match the specified version, got #{vsn}"
@@ -57,13 +68,10 @@ defmodule Mix.Tasks.Deps do
     "#{app} #{version}[#{opts}]"
   end
 
-  @doc """
-
-  """
   def run(_) do
     shell = Mix.shell
 
-    Enum.map all, fn(dep) ->
+    Enum.each all, fn(dep) ->
       shell.info "* #{format_dep(dep)}"
       shell.info "  #{format_status elem(dep, 4)}"
     end
@@ -97,11 +105,11 @@ defmodule Mix.Tasks.Deps do
 
   defp status(scm, app, req, _) do
     deps_path = deps_path(app)
-    if scm.cloned? deps_path do
+    if scm.available? deps_path do
       app_path = File.join deps_path, "ebin/#{app}.app"
       validate_app_file(app_path, app, req)
     else
-      { :uncloned, deps_path }
+      { :unavailable, deps_path }
     end
   end
 
diff --git a/lib/mix/lib/mix/tasks/deps.get.ex b/lib/mix/lib/mix/tasks/deps.get.ex
index 45d25005e6..4d03cf9326 100644
--- a/lib/mix/lib/mix/tasks/deps.get.ex
+++ b/lib/mix/lib/mix/tasks/deps.get.ex
@@ -1,5 +1,5 @@
 defmodule Mix.Tasks.Deps.Get do
   use Mix.Task
 
-  @shortdoc "Get uncloned dependencies"
+  @shortdoc "Get all unavailable dependencies"
 end
\ No newline at end of file
diff --git a/lib/mix/test/mix/tasks/deps_test.exs b/lib/mix/test/mix/tasks/deps_test.exs
index a1beb1d2c8..efd6fc2bfb 100644
--- a/lib/mix/test/mix/tasks/deps_test.exs
+++ b/lib/mix/test/mix/tasks/deps_test.exs
@@ -17,7 +17,28 @@ defmodule Mix.Tasks.DepsTest do
     end
   end
 
-  test "mix deps prints list of dependencies and their status" do
+  defmodule SuccessfulDepsApp do
+    def project do
+      [
+        deps: [
+          { "ok", "0.1.0", git: "https://github.com/elixir-lang/ok.git" }
+        ]
+      ]
+    end
+  end
+
+  defmodule UnclonedDepsApp do
+    def project do
+      [
+        deps: [
+          { "uncloned", "0.1.0",   git: "https://github.com/elixir-lang/uncloned.git" }
+        ]
+      ]
+    end
+  end
+
+
+  test "prints list of dependencies and their status" do
     Mix.Project.push DepsApp
 
     in_fixture "deps_status", fn ->
@@ -32,7 +53,56 @@ defmodule Mix.Tasks.DepsTest do
       assert_received { :mix_shell, :info, ["* noappfile [git: \"https://github.com/elixir-lang/noappfile.git\"]"] }
       assert_received { :mix_shell, :info, ["  could not find app file at deps/noappfile/ebin/noappfile.app"] }
       assert_received { :mix_shell, :info, ["* uncloned [git: \"https://github.com/elixir-lang/uncloned.git\"]"] }
-      assert_received { :mix_shell, :info, ["  the dependency is not checked out at: deps/uncloned"] }
+      assert_received { :mix_shell, :info, ["  the dependency is not available, run `mix deps.get`"] }
+    end
+  after
+    Mix.Project.pop
+  end
+
+  test "check list of dependencies and their status on success" do
+    Mix.Project.push SuccessfulDepsApp
+
+    in_fixture "deps_status", fn ->
+      Mix.Tasks.Deps.Check.run []
+    end
+  after
+    Mix.Project.pop
+  end
+
+  test "check list of dependencies and their status on first run" do
+    Mix.Project.push UnclonedDepsApp
+
+    in_fixture "deps_status", fn ->
+      assert_raise Mix.NotMetDepsError, "Dependencies are not available, run `mix deps.get` before proceeding", fn ->
+        Mix.Tasks.Deps.Check.run []
+      end
+
+      refute_received { :mix_shell, :error, ["* uncloned [git: \"https://github.com/elixir-lang/uncloned.git\"]"] }
+      refute_received { :mix_shell, :error, ["  the dependency is not available, run `mix deps.get`"] }
+    end
+  after
+    Mix.Project.pop
+  end
+
+  test "check list of dependencies and their status on failure" do
+    Mix.Project.push DepsApp
+
+    in_fixture "deps_status", fn ->
+      assert_raise Mix.NotMetDepsError, fn ->
+        Mix.Tasks.Deps.Check.run []
+      end
+
+      refute_received { :mix_shell, :error, ["* ok (0.1.0) [git: \"https://github.com/elixir-lang/ok.git\"]"] }
+      refute_received { :mix_shell, :error, ["  ok"] }
+
+      assert_received { :mix_shell, :error, ["* invalidvsn [git: \"https://github.com/elixir-lang/invalidvsn.git\"]"] }
+      assert_received { :mix_shell, :error, ["  the dependency does not match the specified version, got 0.1.0"] }
+      assert_received { :mix_shell, :error, ["* invalidapp [git: \"https://github.com/elixir-lang/invalidapp.git\"]"] }
+      assert_received { :mix_shell, :error, ["  the app file at deps/invalidapp/ebin/invalidapp.app is invalid"] }
+      assert_received { :mix_shell, :error, ["* noappfile [git: \"https://github.com/elixir-lang/noappfile.git\"]"] }
+      assert_received { :mix_shell, :error, ["  could not find app file at deps/noappfile/ebin/noappfile.app"] }
+      assert_received { :mix_shell, :error, ["* uncloned [git: \"https://github.com/elixir-lang/uncloned.git\"]"] }
+      assert_received { :mix_shell, :error, ["  the dependency is not available, run `mix deps.get`"] }
     end
   after
     Mix.Project.pop