diff --git a/lib/spack/spack/platforms/test.py b/lib/spack/spack/platforms/test.py
index 3480275328..32007394b1 100644
--- a/lib/spack/spack/platforms/test.py
+++ b/lib/spack/spack/platforms/test.py
@@ -14,9 +14,9 @@ class Test(Platform):
     if platform.system().lower() == 'darwin':
         binary_formats = ['macho']
 
-    front_end   = 'x86'
-    back_end    = 'x86_64'
-    default     = 'x86_64'
+    front_end   = 'x86_64'
+    back_end    = 'core2'
+    default     = 'core2'
 
     front_os = 'redhat6'
     back_os = 'debian6'
diff --git a/lib/spack/spack/test/concretize.py b/lib/spack/spack/test/concretize.py
index 02305d84b5..b90a948204 100644
--- a/lib/spack/spack/test/concretize.py
+++ b/lib/spack/spack/test/concretize.py
@@ -230,7 +230,7 @@ def test_architecture_inheritance(self):
         spec.concretize()
         assert spec['cmake'].architecture == spec.architecture
 
-    def test_architecture_deep_inheritance(self):
+    def test_architecture_deep_inheritance(self, mock_targets):
         """Make sure that indirect dependencies receive architecture
         information from the root even when partial architecture information
         is provided by an intermediate dependency.
@@ -243,7 +243,7 @@ def test_architecture_deep_inheritance(self):
         mock_repo.add_package('foopkg', [barpkg], [default_dep])
 
         with spack.repo.swap(mock_repo):
-            spec = Spec('foopkg %clang@3.3 os=CNL target=footar' +
+            spec = Spec('foopkg %gcc@4.5.0 os=CNL target=nocona' +
                         ' ^barpkg os=SuSE11 ^bazpkg os=be')
             spec.concretize()
 
diff --git a/lib/spack/spack/test/conftest.py b/lib/spack/spack/test/conftest.py
index af77684329..0a9d1e6a7b 100644
--- a/lib/spack/spack/test/conftest.py
+++ b/lib/spack/spack/test/conftest.py
@@ -8,6 +8,7 @@
 import errno
 import inspect
 import itertools
+import json
 import os
 import os.path
 import shutil
@@ -17,6 +18,8 @@
 import py
 import pytest
 
+import llnl.util.cpu.microarchitecture
+import llnl.util.cpu.schema
 from llnl.util.filesystem import mkdirp, remove_linked_tree
 
 import spack.architecture
@@ -448,6 +451,40 @@ def default_config():
         yield defaults_config
 
 
+@pytest.fixture(scope='session')
+def mock_uarch_json(tmpdir_factory):
+    """Mock microarchitectures.json with test architecture descriptions."""
+    tmpdir = tmpdir_factory.mktemp('microarchitectures')
+
+    uarch_json = py.path.local(spack.paths.test_path).join(
+        "data", "microarchitectures", "microarchitectures.json")
+    uarch_json.copy(tmpdir)
+    yield str(tmpdir.join("microarchitectures.json"))
+
+
+@pytest.fixture(scope='session')
+def mock_uarch_configuration(mock_uarch_json):
+    """Create mock dictionaries for the llnl.util.cpu."""
+    def load_json():
+        with open(mock_uarch_json) as f:
+            return json.load(f)
+
+    targets_json = llnl.util.cpu.schema.LazyDictionary(load_json)
+    targets = llnl.util.cpu.microarchitecture.LazyDictionary(
+        llnl.util.cpu.microarchitecture._known_microarchitectures)
+
+    yield targets_json, targets
+
+
+@pytest.fixture(scope='function')
+def mock_targets(mock_uarch_configuration, monkeypatch):
+    """Use this fixture to enable mock uarch targets for testing."""
+    targets_json, targets = mock_uarch_configuration
+
+    monkeypatch.setattr(llnl.util.cpu.schema, "targets_json", targets_json)
+    monkeypatch.setattr(llnl.util.cpu.microarchitecture, "targets", targets)
+
+
 @pytest.fixture(scope='session')
 def configuration_dir(tmpdir_factory, linux_os):
     """Copies mock configuration files in a temporary directory. Returns the
diff --git a/lib/spack/spack/test/data/microarchitectures/microarchitectures.json b/lib/spack/spack/test/data/microarchitectures/microarchitectures.json
new file mode 100644
index 0000000000..690d49ffdc
--- /dev/null
+++ b/lib/spack/spack/test/data/microarchitectures/microarchitectures.json
@@ -0,0 +1,486 @@
+{
+  "microarchitectures": {
+    "x86": {
+      "from": null,
+      "vendor": "generic",
+      "features": []
+    },
+    "i686": {
+      "from": "x86",
+      "vendor": "GenuineIntel",
+      "features": []
+    },
+    "pentium2": {
+      "from": "i686",
+      "vendor": "GenuineIntel",
+      "features": [
+        "mmx"
+      ]
+    },
+    "pentium3": {
+      "from": "pentium2",
+      "vendor": "GenuineIntel",
+      "features": [
+        "mmx",
+        "sse"
+      ]
+    },
+    "pentium4": {
+      "from": "pentium3",
+      "vendor": "GenuineIntel",
+      "features": [
+        "mmx",
+        "sse",
+        "sse2"
+      ]
+    },
+    "prescott": {
+      "from": "pentium4",
+      "vendor": "GenuineIntel",
+      "features": [
+        "mmx",
+        "sse",
+        "sse2",
+        "sse3"
+      ]
+    },
+    "x86_64": {
+      "from": null,
+      "vendor": "generic",
+      "features": [],
+      "compilers": {
+        "gcc": [
+          {
+            "versions": "4.2.0:",
+            "name": "x86-64",
+            "flags": "-march={name} -mtune=generic"
+          },
+          {
+            "versions": ":4.1.2",
+            "name": "x86-64",
+            "flags": "-march={name} -mtune={name}"
+          }
+        ],
+        "clang": [
+          {
+            "versions": "0.0.0-apple:",
+            "name": "x86-64",
+            "flags": "-march={name}"
+          },
+          {
+            "versions": ":",
+            "name": "x86-64",
+            "flags": "-march={name} -mtune=generic"
+          }
+        ],
+        "intel": {
+          "versions": ":",
+          "name": "pentium4",
+          "flags": "-march={name} -mtune=generic"
+        }
+      }
+    },
+    "nocona": {
+      "from": "x86_64",
+      "vendor": "GenuineIntel",
+      "features": [
+        "mmx",
+        "sse",
+        "sse2",
+        "sse3"
+      ],
+      "compilers": {
+        "gcc": {
+          "versions": "4.0.4:",
+          "flags": "-march={name} -mtune={name}"
+        },
+        "clang": {
+          "versions": "3.9:",
+          "flags": "-march={name} -mtune={name}"
+        },
+        "intel": {
+          "versions": "16.0:",
+          "name": "pentium4",
+          "flags": "-march={name} -mtune=generic"
+        }
+      }
+    },
+    "core2": {
+      "from": "nocona",
+      "vendor": "GenuineIntel",
+      "features": [
+        "mmx",
+        "sse",
+        "sse2",
+        "ssse3"
+      ],
+      "compilers": {
+        "gcc": {
+          "versions": "4.3.0:",
+          "flags": "-march={name} -mtune={name}"
+        },
+        "clang": {
+          "versions": "3.9:",
+          "flags": "-march={name} -mtune={name}"
+        },
+        "intel": {
+          "versions": "16.0:",
+          "flags": "-march={name} -mtune={name}}"
+        }
+      }
+    },
+    "nehalem": {
+      "from": "core2",
+      "vendor": "GenuineIntel",
+      "features": [
+        "mmx",
+        "sse",
+        "sse2",
+        "ssse3",
+        "sse4_1",
+        "sse4_2",
+        "popcnt"
+      ],
+      "compilers": {
+        "gcc": [
+          {
+            "versions": "4.9:",
+            "flags": "-march={name} -mtune={name}"
+          },
+          {
+            "versions": "4.6:4.8.5",
+            "name": "corei7",
+            "flags": "-march={name} -mtune={name}"
+          }
+        ],
+        "clang": {
+          "versions": "3.9:",
+          "flags": "-march={name} -mtune={name}"
+        },
+        "intel": {
+          "versions": "16.0:",
+          "name": "corei7",
+          "flags": "-march={name} -mtune={name}"
+        }
+      }
+    },
+    "westmere": {
+      "from": "nehalem",
+      "vendor": "GenuineIntel",
+      "features": [
+        "mmx",
+        "sse",
+        "sse2",
+        "ssse3",
+        "sse4_1",
+        "sse4_2",
+        "popcnt",
+        "aes",
+        "pclmulqdq"
+      ],
+      "compilers": {
+        "gcc": {
+          "versions": "4.9:",
+          "flags": "-march={name} -mtune={name}"
+        },
+        "clang": {
+          "versions": "3.9:",
+          "flags": "-march={name} -mtune={name}"
+        },
+        "intel": {
+          "versions": "16.0:",
+          "name": "corei7",
+          "flags": "-march={name} -mtune={name}"
+        }
+      }
+    },
+    "sandybridge": {
+      "from": "westmere",
+      "vendor": "GenuineIntel",
+      "features": [
+        "mmx",
+        "sse",
+        "sse2",
+        "ssse3",
+        "sse4_1",
+        "sse4_2",
+        "popcnt",
+        "aes",
+        "pclmulqdq",
+        "avx"
+      ],
+      "compilers": {
+        "gcc": [
+          {
+            "versions": "4.9:",
+            "flags": "-march={name} -mtune={name}"
+          },
+          {
+            "versions": "4.6:4.8.5",
+            "name": "corei7-avx",
+            "flags": "-march={name} -mtune={name}"
+          }
+        ],
+        "clang": {
+          "versions": "3.9:",
+          "flags": "-march={name} -mtune={name}"
+        },
+        "intel": [
+          {
+            "versions": "16.0:17.9.0",
+            "name": "corei7-avx",
+            "flags": "-march={name} -mtune={name}"
+          },
+          {
+            "versions": "18.0:",
+            "flags": "-march={name} -mtune={name}"
+          }
+        ]
+      }
+    },
+    "ivybridge": {
+      "from": "sandybridge",
+      "vendor": "GenuineIntel",
+      "features": [
+        "mmx",
+        "sse",
+        "sse2",
+        "ssse3",
+        "sse4_1",
+        "sse4_2",
+        "popcnt",
+        "aes",
+        "pclmulqdq",
+        "avx",
+        "rdrand",
+        "f16c"
+      ],
+      "compilers": {
+        "gcc": [
+          {
+            "versions": "4.9:",
+            "flags": "-march={name} -mtune={name}"
+          },
+          {
+            "versions": "4.6:4.8.5",
+            "name": "core-avx-i",
+            "flags": "-march={name} -mtune={name}"
+          }
+        ],
+        "clang": {
+          "versions": "3.9:",
+          "flags": "-march={name} -mtune={name}"
+        },
+        "intel": [
+          {
+            "versions": "16.0:17.9.0",
+            "name": "core-avx-i",
+            "flags": "-march={name} -mtune={name}"
+          },
+          {
+            "versions": "18.0:",
+            "flags": "-march={name} -mtune={name}"
+          }
+        ]
+      }
+    },
+    "haswell": {
+      "from": "ivybridge",
+      "vendor": "GenuineIntel",
+      "features": [
+        "mmx",
+        "sse",
+        "sse2",
+        "ssse3",
+        "sse4_1",
+        "sse4_2",
+        "popcnt",
+        "aes",
+        "pclmulqdq",
+        "avx",
+        "rdrand",
+        "f16c",
+        "movbe",
+        "fma",
+        "avx2",
+        "bmi1",
+        "bmi2"
+      ],
+      "compilers": {
+        "gcc": [
+          {
+            "versions": "4.9:",
+            "flags": "-march={name} -mtune={name}"
+          },
+          {
+            "versions": "4.8:4.8.5",
+            "name": "core-avx2",
+            "flags": "-march={name} -mtune={name}"
+          }
+        ],
+        "clang": {
+          "versions": "3.9:",
+          "flags": "-march={name} -mtune={name}"
+        },
+        "intel": [
+          {
+            "versions": "16.0:17.9.0",
+            "name": "core-avx2",
+            "flags": "-march={name} -mtune={name}"
+          },
+          {
+            "versions": "18.0:",
+            "flags": "-march={name} -mtune={name}"
+          }
+        ]
+      }
+    },
+    "broadwell": {
+      "from": "haswell",
+      "vendor": "GenuineIntel",
+      "features": [
+        "mmx",
+        "sse",
+        "sse2",
+        "ssse3",
+        "sse4_1",
+        "sse4_2",
+        "popcnt",
+        "aes",
+        "pclmulqdq",
+        "avx",
+        "rdrand",
+        "f16c",
+        "movbe",
+        "fma",
+        "avx2",
+        "bmi1",
+        "bmi2",
+        "rdseed",
+        "adx"
+      ],
+      "compilers": {
+        "gcc": {
+          "versions": "4.9:",
+          "flags": "-march={name} -mtune={name}"
+        },
+        "clang": {
+          "versions": "3.9:",
+          "flags": "-march={name} -mtune={name}"
+        },
+        "intel": {
+          "versions": "18.0:",
+          "flags": "-march={name} -mtune={name}"
+        }
+      }
+    },
+    "skylake": {
+      "from": "broadwell",
+      "vendor": "GenuineIntel",
+      "features": [
+        "mmx",
+        "sse",
+        "sse2",
+        "ssse3",
+        "sse4_1",
+        "sse4_2",
+        "popcnt",
+        "aes",
+        "pclmulqdq",
+        "avx",
+        "rdrand",
+        "f16c",
+        "movbe",
+        "fma",
+        "avx2",
+        "bmi1",
+        "bmi2",
+        "rdseed",
+        "adx",
+        "clflushopt",
+        "xsavec",
+        "xsaveopt"
+      ],
+      "compilers": {
+        "gcc": {
+          "versions": "6.0:",
+          "flags": "-march={name} -mtune={name}"
+        },
+        "clang": {
+          "versions": "3.9:",
+          "flags": "-march={name} -mtune={name}"
+        },
+        "intel": {
+          "versions": "18.0:",
+          "flags": "-march={name} -mtune={name}"
+        }
+      }
+    }
+  },
+  "feature_aliases": {
+    "sse3": {
+      "reason": "ssse3 is a superset of sse3 and might be the only one listed",
+      "any_of": [
+        "ssse3"
+      ]
+    },
+    "avx512": {
+      "reason": "avx512 indicates generic support for any of the avx512 instruction sets",
+      "any_of": [
+        "avx512f",
+        "avx512vl",
+        "avx512bw",
+        "avx512dq",
+        "avx512cd"
+      ]
+    },
+    "fma": {
+      "reason": "FMA has been supported by PowerISA since Power1, but might not be listed in features",
+      "families": [
+        "ppc64le",
+        "ppc64"
+      ]
+    },
+    "sse4.1": {
+      "reason": "permits to refer to sse4_1 also as sse4.1",
+      "any_of": [
+        "sse4_1"
+      ]
+    },
+    "sse4.2": {
+      "reason": "permits to refer to sse4_2 also as sse4.2",
+      "any_of": [
+        "sse4_2"
+      ]
+    }
+  },
+  "conversions": {
+    "description": "Conversions that map some platform specific values to canonical values",
+    "arm_vendors": {
+      "0x41": "ARM",
+      "0x42": "Broadcom",
+      "0x43": "Cavium",
+      "0x44": "DEC",
+      "0x46": "Fujitsu",
+      "0x48": "HiSilicon",
+      "0x49": "Infineon Technologies AG",
+      "0x4d": "Motorola",
+      "0x4e": "Nvidia",
+      "0x50": "APM",
+      "0x51": "Qualcomm",
+      "0x53": "Samsung",
+      "0x56": "Marvell",
+      "0x61": "Apple",
+      "0x66": "Faraday",
+      "0x68": "HXT",
+      "0x69": "Intel"
+    },
+    "darwin_flags": {
+      "sse4.1": "sse4_1",
+      "sse4.2": "sse4_2",
+      "avx1.0": "avx",
+      "clfsopt": "clflushopt",
+      "xsave": "xsavec xsaveopt"
+    }
+  }
+}
diff --git a/lib/spack/spack/test/spec_semantics.py b/lib/spack/spack/test/spec_semantics.py
index 4d221378c7..330a1d7a0a 100644
--- a/lib/spack/spack/test/spec_semantics.py
+++ b/lib/spack/spack/test/spec_semantics.py
@@ -965,8 +965,8 @@ def test_abstract_spec_prefix_error(self):
         with pytest.raises(SpecError):
             spec.prefix
 
-    def test_forwarding_of_architecture_attributes(self):
-        spec = Spec('libelf').concretized()
+    def test_forwarding_of_architecture_attributes(self, mock_targets):
+        spec = Spec('libelf target=x86_64').concretized()
 
         # Check that we can still access each member through
         # the architecture attribute