diff --git a/README.md b/README.md
index 6c4ef15..bad24b2 100644
--- a/README.md
+++ b/README.md
@@ -9,10 +9,20 @@ It's a work in progress.
 
 Add it as a compiler plugin in your project, or run `sbt console` in this project to see it in action.
 
+The plugin can optionally use a properties file (provided with `-P
+linter:config:/path/to/it` on the scalac command line) that allows
+controlling the action taken by the plugin either globally or on a
+per-warning basis. The default action is `warn` and may be changed to
+`no_action` or `error` by setting the `default_action` value in the
+properties file.  The default can be overridden on a per-check basis
+with any of those three options.
+
 ## Currently suported warnings
 
 ### Unsafe `==`
 
+The configuration property is `check.unsafe_equals`.
+
     scala> Nil == None
     <console>:29: warning: Comparing with == on instances of different types (object Nil, object None) will probably return false.
                   Nil == None
@@ -20,6 +30,8 @@ Add it as a compiler plugin in your project, or run `sbt console` in this projec
 
 ### Unsafe `contains`
 
+The configuration property is `check.unsafe_contains`.
+
     scala> List(1, 2, 3).contains("4")
     <console>:29: warning: SeqLike[Int].contains(java.lang.String) will probably return false.
                   List(1, 2, 3).contains("4")
@@ -28,6 +40,8 @@ Add it as a compiler plugin in your project, or run `sbt console` in this projec
 
 ### Wildcard import from `scala.collection.JavaConversions`
 
+The configuration property is `check.java_conversions`.
+
     scala> import scala.collection.JavaConversions._
     <console>:29: warning: Conversions in scala.collection.JavaConversions._ are dangerous.
            import scala.collection.JavaConversions._
@@ -35,6 +49,8 @@ Add it as a compiler plugin in your project, or run `sbt console` in this projec
 
 ### Calling `Option#get`
 
+The configuration property is `check.option_get`.
+
     scala> Option(1).get
     <console>:29: warning: Calling .get on Option will throw an exception if the Option is None.
                   Option(1).get
@@ -43,8 +59,6 @@ Add it as a compiler plugin in your project, or run `sbt console` in this projec
 ## Future Work
 
 * Add more warnings
-* Pick and choose which warnings you want
-* Choose whether they should be warnings or errors
 
 ### Ideas for new warnings
 
diff --git a/src/main/scala/JavaConversions.scala b/src/main/scala/JavaConversions.scala
new file mode 100644
index 0000000..d4a80c2
--- /dev/null
+++ b/src/main/scala/JavaConversions.scala
@@ -0,0 +1,19 @@
+package com.foursquare.lint
+
+import scala.tools.nsc.Global
+
+class JavaConversions(g: Global) extends LinterAction(g, Warnings.JavaConversions) {
+  import global._
+
+  val JavaConversionsModule: Symbol = definitions.getModule("scala.collection.JavaConversions")
+
+  def isGlobalImport(selector: ImportSelector): Boolean = {
+    selector.name == nme.WILDCARD && selector.renamePos == -1
+  }
+
+  val action: PartialFunction[Tree, (Position, String)] = {
+    case Import(pkg, selectors)
+        if pkg.symbol == JavaConversionsModule && selectors.exists(isGlobalImport) =>
+      (pkg.pos, "Conversions in scala.collection.JavaConversions._ are dangerous.")
+  }
+}
diff --git a/src/main/scala/LinterAction.scala b/src/main/scala/LinterAction.scala
new file mode 100644
index 0000000..e5416ae
--- /dev/null
+++ b/src/main/scala/LinterAction.scala
@@ -0,0 +1,15 @@
+package com.foursquare.lint
+
+import scala.tools.nsc.Global
+
+abstract class LinterAction(val global: Global, val warning: Warnings.Warning) {
+  import global._
+
+  def action: PartialFunction[Tree, (Position, String)]
+
+  // Utility predicates that are used by multiple warning types
+
+  def methodImplements(method: Symbol, target: Symbol): Boolean = {
+    method == target || method.allOverriddenSymbols.contains(target)
+  }
+}
diff --git a/src/main/scala/LinterPlugin.scala b/src/main/scala/LinterPlugin.scala
index ec73b4c..eb08a78 100644
--- a/src/main/scala/LinterPlugin.scala
+++ b/src/main/scala/LinterPlugin.scala
@@ -20,74 +20,116 @@ import scala.reflect.generic.Flags
 import scala.tools.nsc.{Global, Phase}
 import scala.tools.nsc.plugins.{Plugin, PluginComponent}
 
+import java.io.{InputStream, FileInputStream, IOException}
+
 class LinterPlugin(val global: Global) extends Plugin {
   import global._
 
   val name = "linter"
   val description = ""
   val components = List[PluginComponent](LinterComponent)
+  var warningActions = (_: Warnings.Warning) => Actions.Warn
 
-  private object LinterComponent extends PluginComponent {
-    import global._
-
-    val global = LinterPlugin.this.global
+  def warningEnabled(warning: Warnings.Warning) = warningActions(warning) != Actions.NoAction
 
-    override val runsAfter = List("typer")
+  object Actions extends Enumeration {
+    type Action = Value
+    val NoAction,
+        Warn,
+        Error = Value
+  }
 
-    val phaseName = "linter"
+  val OptionConfig = "config:"
 
-    override def newPhase(prev: Phase): StdPhase = new StdPhase(prev) {
-      override def apply(unit: global.CompilationUnit): Unit = {
-        new LinterTraverser(unit).traverse(unit.body)
-      }
+  override def processOptions(options: List[String], error: String => Unit) {
+    for(option <- options) {
+      if(option.startsWith(OptionConfig)) loadConfiguration(option.drop(OptionConfig.length), error)
+      else error("Unknown option: " + option)
     }
+  }
 
-    class LinterTraverser(unit: CompilationUnit) extends Traverser {
-      import definitions.{AnyClass, ObjectClass, Object_==, OptionClass, SeqClass}
+  private def underscoreify(camelCase: String): String = // not super-smart, but sufficient unto the purpose
+    camelCase.replaceAll("([A-Z])","_$1").toLowerCase.dropWhile(_ == '_')
 
-      val JavaConversionsModule: Symbol = definitions.getModule("scala.collection.JavaConversions")
-      val SeqLikeClass: Symbol = definitions.getClass("scala.collection.SeqLike")
-      val SeqLikeContains: Symbol = SeqLikeClass.info.member(newTermName("contains"))
-      val OptionGet: Symbol = OptionClass.info.member(nme.get)
+  private def loadConfiguration(filename: String, error: String => Unit) {
+    import java.util.Properties
+    import scala.collection.JavaConverters._
 
-      def SeqMemberType(seenFrom: Type): Type = {
-        SeqLikeClass.tpe.typeArgs.head.asSeenFrom(seenFrom, SeqLikeClass)
-      }
+    val props = new Properties
 
-      def isSubtype(x: Tree, y: Tree): Boolean = {
-        x.tpe.widen <:< y.tpe.widen
+    try {
+      val stream = openPropertiesFile(filename)
+      try {
+        props.load(stream)
+      } finally {
+        stream.close()
       }
+    } catch {
+      case e: IOException =>
+        error("Exception occurred while loading properties file: " + e.getMessage)
+        return
+    }
 
-      def methodImplements(method: Symbol, target: Symbol): Boolean = {
-        method == target || method.allOverriddenSymbols.contains(target)
-      }
+    val NoAction = underscoreify(Actions.NoAction.toString)
+    val Warn = underscoreify(Actions.Warn.toString)
+    val Error = underscoreify(Actions.Error.toString)
 
-      def isGlobalImport(selector: ImportSelector): Boolean = {
-        selector.name == nme.WILDCARD && selector.renamePos == -1
+    val defaultAction = props.getProperty("default_action", Warn) match {
+      case action@(NoAction|Warn|Error) => action
+      case other =>
+        error("Unknown action for default_action: " + other)
+        return
+    }
+
+    warningActions =
+      Warnings.values.foldLeft(Map.empty[Warnings.Warning, Actions.Action]) { (warningConfig, warning) =>
+        val action = props.getProperty("check." + underscoreify(warning.toString), defaultAction) match {
+          case NoAction => Actions.NoAction
+          case Warn => Actions.Warn
+          case Error => Actions.Error
+          case other =>
+            error("Unknown action for warning " + warning + ": " + other)
+            return
+        }
+        warningConfig + (warning -> action)
       }
+  }
+
+  protected def openPropertiesFile(filename: String): InputStream =
+    new FileInputStream(filename)
 
-      override def traverse(tree: Tree): Unit = tree match {
-        case Apply(eqeq @ Select(lhs, nme.EQ), List(rhs))
-            if methodImplements(eqeq.symbol, Object_==) && !(isSubtype(lhs, rhs) || isSubtype(rhs, lhs)) =>
-          val warnMsg = "Comparing with == on instances of different types (%s, %s) will probably return false."
-          unit.warning(eqeq.pos, warnMsg.format(lhs.tpe.widen, rhs.tpe.widen))
+  private object LinterComponent extends PluginComponent {
+    import global._
+
+    val global = LinterPlugin.this.global
 
-        case Import(pkg, selectors)
-            if pkg.symbol == JavaConversionsModule && selectors.exists(isGlobalImport) =>
-          unit.warning(pkg.pos, "Conversions in scala.collection.JavaConversions._ are dangerous.")
+    override val runsAfter = List("typer")
 
-        case Apply(contains @ Select(seq, _), List(target))
-            if methodImplements(contains.symbol, SeqLikeContains) && !(target.tpe <:< SeqMemberType(seq.tpe)) =>
-          val warnMsg = "SeqLike[%s].contains(%s) will probably return false."
-          unit.warning(contains.pos, warnMsg.format(SeqMemberType(seq.tpe), target.tpe.widen))
+    val phaseName = "linter"
 
-        case get @ Select(_, nme.get) if methodImplements(get.symbol, OptionGet) =>
-          if (!get.pos.source.path.contains("src/test")) {
-            unit.warning(get.pos, "Calling .get on Option will throw an exception if the Option is None.")
-          }
+    override def newPhase(prev: Phase): StdPhase = new StdPhase(prev) {
+      override def apply(unit: global.CompilationUnit): Unit = {
+        new LinterTraverser(unit).traverse(unit.body)
+      }
+    }
 
-        case _ =>
-          super.traverse(tree)
+    class LinterTraverser(unit: CompilationUnit) extends Traverser {
+      val actions = List(new UnsafeEquals(global),
+                         new UnsafeContains(global),
+                         new OptionGet(global),
+                         new JavaConversions(global)).filter(a => warningEnabled(a.warning))
+
+      override def traverse(tree: Tree): Unit = {
+        // I hate thes .asInstanceOfs.  But I cannot convince the
+        // compiler to thread the dependent types through!
+        actions.find(a => a.action.isDefinedAt(tree.asInstanceOf[a.global.Tree])) match {
+          case Some(action) =>
+            val (pos, msg) = action.action(tree.asInstanceOf[action.global.Tree])
+            if(warningActions(action.warning) == Actions.Error) unit.error(pos, msg)
+            else unit.warning(pos, msg)
+          case None =>
+            super.traverse(tree)
+        }
       }
     }
   }
diff --git a/src/main/scala/OptionGet.scala b/src/main/scala/OptionGet.scala
new file mode 100644
index 0000000..e06210b
--- /dev/null
+++ b/src/main/scala/OptionGet.scala
@@ -0,0 +1,16 @@
+package com.foursquare.lint
+
+import scala.tools.nsc.Global
+
+class OptionGet(g: Global) extends LinterAction(g, Warnings.OptionGet) {
+  import global._
+
+  import definitions.OptionClass
+  val OptionGet: Symbol = OptionClass.info.member(nme.get)
+
+  val action: PartialFunction[Tree, (Position, String)] = {
+    case get @ Select(_, nme.get)
+        if methodImplements(get.symbol, OptionGet) && !get.pos.source.path.contains("src/test") =>
+      (get.pos, "Calling .get on Option will throw an exception if the Option is None.")
+  }
+}
diff --git a/src/main/scala/UnsafeContains.scala b/src/main/scala/UnsafeContains.scala
new file mode 100644
index 0000000..bda17a2
--- /dev/null
+++ b/src/main/scala/UnsafeContains.scala
@@ -0,0 +1,21 @@
+package com.foursquare.lint
+
+import scala.tools.nsc.Global
+
+class UnsafeContains(g: Global) extends LinterAction(g, Warnings.UnsafeContains) {
+  import global._
+
+  val SeqLikeClass: Symbol = definitions.getClass("scala.collection.SeqLike")
+  val SeqLikeContains: Symbol = SeqLikeClass.info.member(newTermName("contains"))
+
+  def SeqMemberType(seenFrom: Type): Type = {
+    SeqLikeClass.tpe.typeArgs.head.asSeenFrom(seenFrom, SeqLikeClass)
+  }
+
+  val action: PartialFunction[Tree, (Position, String)] = {
+    case Apply(contains @ Select(seq, _), List(target))
+        if methodImplements(contains.symbol, SeqLikeContains) && !(target.tpe <:< SeqMemberType(seq.tpe)) =>
+      val warnMsg = "SeqLike[%s].contains(%s) will probably return false."
+      (contains.pos, warnMsg.format(SeqMemberType(seq.tpe), target.tpe.widen))
+  }
+}
diff --git a/src/main/scala/UnsafeEquals.scala b/src/main/scala/UnsafeEquals.scala
new file mode 100644
index 0000000..c06f77a
--- /dev/null
+++ b/src/main/scala/UnsafeEquals.scala
@@ -0,0 +1,20 @@
+package com.foursquare.lint
+
+import scala.tools.nsc.Global
+
+class UnsafeEquals(g: Global) extends LinterAction(g, Warnings.UnsafeEquals) {
+  import global._
+  import definitions.Object_==
+
+  def isSubtype(x: Tree, y: Tree): Boolean = {
+    x.tpe.widen <:< y.tpe.widen
+  }
+
+  val action: PartialFunction[Tree, (Position, String)] = {
+    case Apply(eqeq @ Select(lhs, nme.EQ), List(rhs))
+        if methodImplements(eqeq.symbol, Object_==) && !(isSubtype(lhs, rhs) || isSubtype(rhs, lhs)) =>
+      val warnMsg = "Comparing with == on instances of different types (%s, %s) will probably return false."
+      (eqeq.pos, warnMsg.format(lhs.tpe.widen, rhs.tpe.widen))
+  }
+}
+
diff --git a/src/main/scala/Warnings.scala b/src/main/scala/Warnings.scala
new file mode 100644
index 0000000..9610d91
--- /dev/null
+++ b/src/main/scala/Warnings.scala
@@ -0,0 +1,9 @@
+package com.foursquare.lint
+
+object Warnings extends Enumeration {
+  type Warning = Value
+  val JavaConversions,
+  OptionGet,
+  UnsafeContains,
+  UnsafeEquals = Value
+}
diff --git a/src/test/resources/testprops/allbutjavaconversionserror.properties b/src/test/resources/testprops/allbutjavaconversionserror.properties
new file mode 100644
index 0000000..98a038a
--- /dev/null
+++ b/src/test/resources/testprops/allbutjavaconversionserror.properties
@@ -0,0 +1,3 @@
+check.option_get = error
+check.unsafe_contains = error
+check.unsafe_equals = error
diff --git a/src/test/resources/testprops/allbutjavaconversionsoff.properties b/src/test/resources/testprops/allbutjavaconversionsoff.properties
new file mode 100644
index 0000000..153bf52
--- /dev/null
+++ b/src/test/resources/testprops/allbutjavaconversionsoff.properties
@@ -0,0 +1,3 @@
+check.option_get = no_action
+check.unsafe_contains = no_action
+check.unsafe_equals = no_action
diff --git a/src/test/resources/testprops/allbutoptiongeterror.properties b/src/test/resources/testprops/allbutoptiongeterror.properties
new file mode 100644
index 0000000..f109939
--- /dev/null
+++ b/src/test/resources/testprops/allbutoptiongeterror.properties
@@ -0,0 +1,3 @@
+check.java_conversions = error
+check.unsafe_contains = error
+check.unsafe_equals = error
diff --git a/src/test/resources/testprops/allbutoptiongetoff.properties b/src/test/resources/testprops/allbutoptiongetoff.properties
new file mode 100644
index 0000000..3902ad9
--- /dev/null
+++ b/src/test/resources/testprops/allbutoptiongetoff.properties
@@ -0,0 +1,3 @@
+check.java_conversions = no_action
+check.unsafe_contains = no_action
+check.unsafe_equals = no_action
diff --git a/src/test/resources/testprops/allbutunsafecontainserror.properties b/src/test/resources/testprops/allbutunsafecontainserror.properties
new file mode 100644
index 0000000..0293136
--- /dev/null
+++ b/src/test/resources/testprops/allbutunsafecontainserror.properties
@@ -0,0 +1,3 @@
+check.java_conversions = error
+check.option_get = error
+check.unsafe_equals = error
diff --git a/src/test/resources/testprops/allbutunsafecontainsoff.properties b/src/test/resources/testprops/allbutunsafecontainsoff.properties
new file mode 100644
index 0000000..90d0c10
--- /dev/null
+++ b/src/test/resources/testprops/allbutunsafecontainsoff.properties
@@ -0,0 +1,3 @@
+check.java_conversions = no_action
+check.option_get = no_action
+check.unsafe_equals = no_action
diff --git a/src/test/resources/testprops/allbutunsafeequalserror.properties b/src/test/resources/testprops/allbutunsafeequalserror.properties
new file mode 100644
index 0000000..e9bb745
--- /dev/null
+++ b/src/test/resources/testprops/allbutunsafeequalserror.properties
@@ -0,0 +1,3 @@
+check.java_conversions = error
+check.option_get = error
+check.unsafe_contains = error
diff --git a/src/test/resources/testprops/allbutunsafeequalsoff.properties b/src/test/resources/testprops/allbutunsafeequalsoff.properties
new file mode 100644
index 0000000..a005828
--- /dev/null
+++ b/src/test/resources/testprops/allbutunsafeequalsoff.properties
@@ -0,0 +1,3 @@
+check.java_conversions = no_action
+check.option_get = no_action
+check.unsafe_contains = no_action
diff --git a/src/test/resources/testprops/allerror.properties b/src/test/resources/testprops/allerror.properties
new file mode 100644
index 0000000..3471c9c
--- /dev/null
+++ b/src/test/resources/testprops/allerror.properties
@@ -0,0 +1,4 @@
+check.java_conversions = error
+check.option_get = error
+check.unsafe_contains = error
+check.unsafe_equals = error
diff --git a/src/test/resources/testprops/alloff.properties b/src/test/resources/testprops/alloff.properties
new file mode 100644
index 0000000..f5a78d1
--- /dev/null
+++ b/src/test/resources/testprops/alloff.properties
@@ -0,0 +1,4 @@
+check.java_conversions = no_action
+check.option_get = no_action
+check.unsafe_contains = no_action
+check.unsafe_equals = no_action
diff --git a/src/test/resources/testprops/defaulterror.properties b/src/test/resources/testprops/defaulterror.properties
new file mode 100644
index 0000000..73a3c79
--- /dev/null
+++ b/src/test/resources/testprops/defaulterror.properties
@@ -0,0 +1 @@
+default_action = error
diff --git a/src/test/resources/testprops/defaultnoaction.properties b/src/test/resources/testprops/defaultnoaction.properties
new file mode 100644
index 0000000..d27dc35
--- /dev/null
+++ b/src/test/resources/testprops/defaultnoaction.properties
@@ -0,0 +1 @@
+default_action = no_action
diff --git a/src/test/resources/testprops/javaconversionserror.properties b/src/test/resources/testprops/javaconversionserror.properties
new file mode 100644
index 0000000..dcd92e5
--- /dev/null
+++ b/src/test/resources/testprops/javaconversionserror.properties
@@ -0,0 +1 @@
+check.java_conversions = error
diff --git a/src/test/resources/testprops/javaconversionsoff.properties b/src/test/resources/testprops/javaconversionsoff.properties
new file mode 100644
index 0000000..9524f53
--- /dev/null
+++ b/src/test/resources/testprops/javaconversionsoff.properties
@@ -0,0 +1 @@
+check.java_conversions = no_action
diff --git a/src/test/resources/testprops/optiongeterror.properties b/src/test/resources/testprops/optiongeterror.properties
new file mode 100644
index 0000000..c0f035a
--- /dev/null
+++ b/src/test/resources/testprops/optiongeterror.properties
@@ -0,0 +1 @@
+check.option_get = error
diff --git a/src/test/resources/testprops/optiongetoff.properties b/src/test/resources/testprops/optiongetoff.properties
new file mode 100644
index 0000000..74c3c7f
--- /dev/null
+++ b/src/test/resources/testprops/optiongetoff.properties
@@ -0,0 +1 @@
+check.option_get = no_action
diff --git a/src/test/resources/testprops/unsafecontainserror.properties b/src/test/resources/testprops/unsafecontainserror.properties
new file mode 100644
index 0000000..9c0cb10
--- /dev/null
+++ b/src/test/resources/testprops/unsafecontainserror.properties
@@ -0,0 +1 @@
+check.unsafe_contains = error
diff --git a/src/test/resources/testprops/unsafecontainsoff.properties b/src/test/resources/testprops/unsafecontainsoff.properties
new file mode 100644
index 0000000..3e36be8
--- /dev/null
+++ b/src/test/resources/testprops/unsafecontainsoff.properties
@@ -0,0 +1 @@
+check.unsafe_contains = no_action
diff --git a/src/test/resources/testprops/unsafeequalserror.properties b/src/test/resources/testprops/unsafeequalserror.properties
new file mode 100644
index 0000000..8f4f815
--- /dev/null
+++ b/src/test/resources/testprops/unsafeequalserror.properties
@@ -0,0 +1 @@
+check.unsafe_equals = error
diff --git a/src/test/resources/testprops/unsafeequalsoff.properties b/src/test/resources/testprops/unsafeequalsoff.properties
new file mode 100644
index 0000000..6089438
--- /dev/null
+++ b/src/test/resources/testprops/unsafeequalsoff.properties
@@ -0,0 +1 @@
+check.unsafe_equals = no_action
diff --git a/src/test/scala/LinterPluginTest.scala b/src/test/scala/LinterPluginTest.scala
index 20b0a00..bcaa3e4 100644
--- a/src/test/scala/LinterPluginTest.scala
+++ b/src/test/scala/LinterPluginTest.scala
@@ -22,7 +22,9 @@ import org.specs.SpecsMatchers
 class LinterPluginTest extends SpecsMatchers {
   var linterPlugin: LinterPlugin = null
 
-  class Compiler {
+  class InitializationException(message: String) extends Exception(message)
+
+  class Compiler(pluginOptions: List[String]) {
     import java.io.{PrintWriter, StringWriter}
     import scala.io.Source
     import scala.tools.nsc.{Global, Settings}
@@ -35,7 +37,7 @@ class LinterPluginTest extends SpecsMatchers {
     settings.bootclasspath.append(Source.fromURL(loader.getResource("boot.class.path")).mkString)
     settings.deprecation.value = true // enable detailed deprecation warnings
     settings.unchecked.value = true // enable detailed unchecked warnings
-    settings.Xwarnfatal.value = true // warnings cause compile failures too
+    settings.Xwarnfatal.value = false // but not this because we're testing the difference between error and warning
 
     val stringWriter = new StringWriter()
 
@@ -46,7 +48,16 @@ class LinterPluginTest extends SpecsMatchers {
         new Global(settings, reporter) {
           override protected def computeInternalPhases () {
             super.computeInternalPhases
-            linterPlugin = new LinterPlugin(this)
+            linterPlugin = new LinterPlugin(this) {
+              override def openPropertiesFile(filename: String) =
+                Option(getClass.getClassLoader.getResourceAsStream(filename)).getOrElse {
+                  throw new java.io.FileNotFoundException("No such file " + filename)
+                }
+            }
+
+            // is this the right place?
+            linterPlugin.processOptions(pluginOptions, msg => throw new InitializationException(msg))
+
             for (phase <- linterPlugin.components)
               phasesSet += phase
           }
@@ -58,18 +69,29 @@ class LinterPluginTest extends SpecsMatchers {
       stringWriter.getBuffer.delete(0, stringWriter.getBuffer.length)
       val thunked = "() => { %s }".format(code)
       interpreter.interpret(thunked) match {
-        case Results.Success => None
-        case Results.Error => Some(stringWriter.toString)
+        case Results.Success if stringWriter.toString.indexOf("warning") == -1 => None
+        case Results.Success | Results.Error => Some(stringWriter.toString)
         case Results.Incomplete => throw new Exception("Incomplete code snippet")
       }
     }
   }
 
-  val compiler = new Compiler
-  def check(code: String, expectedError: Option[String] = None) {
+  val compilerCache = new scala.collection.mutable.HashMap[List[String], Compiler]
+  def compilerFor(options: List[String]): Compiler = {
+    compilerCache.get(options) match {
+      case Some(compiler) => compiler
+      case None =>
+        val compiler = new Compiler(options)
+        compilerCache += options -> compiler
+        compiler
+    }
+  }
+
+  def check(code: String, expectedError: Option[String] = None, options: List[String] = Nil) {
     // Either they should both be None or the expected error should be a
     // substring of the actual error.
-    (expectedError, compiler.compileAndLint(code)) must beLike {
+
+    (expectedError, compilerFor(options).compileAndLint(code)) must beLike {
       case (None, None) => true
       case (Some(exp), Some(act)) => act.contains(exp)
     }
@@ -81,64 +103,92 @@ class LinterPluginTest extends SpecsMatchers {
   }
 
   @Test
-  def testHasVersusContains(): Unit = {
-    val msg = Some("SeqLike[Int].contains(java.lang.String) will probably return false.")
+  def nonExistantFileErrors(): Unit = {
+    check("""1 + 1""", None, List("config:thisfiledoesnotexistimsure")) must throwA[InitializationException]
+  }
 
-    check("""val x = List(4); x.contains("foo")""", msg)
+  @Test
+  def nonBadOptionFileErrors(): Unit = {
+    check("""1 + 1""", None, List("notavalidconfigoption")) must throwA[InitializationException]
+  }
 
-    // Set and Map have type-safe contains methods so we don't want to warn on
-    // those.
-    check("""val x = Set(4); x.contains(3)""", None)
-    check("""val x = Map(4 -> 5); x.contains(3)""", None)
+  def multiTest(message: String, basename: String)(impltest: (Option[String], List[String]) => Unit): Unit = {
+    impltest(Some("warning: " + message), Nil)
+    impltest(None, List("config:testprops/" + basename + "off.properties"))
+    impltest(Some("error: " + message), List("config:testprops/" + basename + "error.properties"))
+    impltest(Some("warning: " + message), List("config:testprops/allbut" + basename + "off.properties"))
+    impltest(Some("warning: " + message), List("config:testprops/allbut" + basename + "error.properties"))
   }
 
   @Test
-  def testNoOptionGet(): Unit = {
-    val msg = Some("Calling .get on Option will throw an exception if the Option is None.")
+  def testHasVersusContains(): Unit = {
+    multiTest("SeqLike[Int].contains(java.lang.String) will probably return false.", "unsafecontains") { (msg, options) =>
+      check("""val x = List(4); x.contains("foo")""", msg, options)
 
-    check("""Option(10).get""", msg)
-    check("""val x: Option[Int] = None ; x.get""", msg)
-    check("""val x: Option[Int] = Some(3); x.get""", msg)
-    check("""val x = None ; x.get""", msg)
-    check("""val x = Some(3) ; x.get""", msg)
+      // Set and Map have type-safe contains methods so we don't want to warn on
+      // those.
+      check("""val x = Set(4); x.contains(3)""", options = options)
+      check("""val x = Map(4 -> 5); x.contains(3)""", options = options)
+    }
+  }
 
-    check("""Map(1 -> "1", 2 -> "2").get(1)""")
+  @Test
+  def testNoOptionGet(): Unit = {
+    multiTest("Calling .get on Option will throw an exception if the Option is None.", "optionget") { (msg, options) =>
+      check("""Option(10).get""", msg, options)
+      check("""val x: Option[Int] = None ; x.get""", msg, options)
+      check("""val x: Option[Int] = Some(3); x.get""", msg, options)
+      check("""val x = None ; x.get""", msg, options)
+      check("""val x = Some(3) ; x.get""", msg, options)
+
+      check("""Map(1 -> "1", 2 -> "2").get(1)""", options = options)
+    }
   }
 
   @Test
   def testJavaConversionsImport(): Unit = {
-    val msg = Some("Conversions in scala.collection.JavaConversions._ are dangerous.")
-
-    check("import scala.collection.JavaConversions._;", msg)
+    multiTest("Conversions in scala.collection.JavaConversions._ are dangerous.", "javaconversions") { (msg, options) =>
+      check("import scala.collection.JavaConversions._;", msg, options)
+    }
   }
 
   @Test
   def testUnsafeEquals(): Unit = {
-    val msg = Some("Comparing with ==")
-
-    // Should warn
-    check("Nil == None", msg)
-    check("""{
-      val x: List[Int] = Nil
-      val y: List[String] = Nil
-      x == y
-    }""", msg)
-
-    // Should compile
-    check(""" "foo" == "bar" """)
-    check("""{
-      val x: List[Int] = Nil
-      val y: List[Int] = Nil
-      x == y
-    }""")
-    check("""{
-      val x: String = "foo"
-      val y: String = "bar"
-      x == y
-    }""")
-    check("""{
-      val x: String = "foo"
-      x == "bar"
-    }""")
+    multiTest("Comparing with ==", "unsafeequals") { (msg, options) =>
+      // Should warn
+      check("Nil == None", msg, options)
+      check("""{
+        val x: List[Int] = Nil
+        val y: List[String] = Nil
+        x == y
+      }""", msg, options)
+
+      // Should compile
+      check(""" "foo" == "bar" """, options = options)
+      check("""{
+        val x: List[Int] = Nil
+        val y: List[Int] = Nil
+        x == y
+      }""", options = options)
+      check("""{
+        val x: String = "foo"
+        val y: String = "bar"
+        x == y
+      }""", options = options)
+      check("""{
+        val x: String = "foo"
+        x == "bar"
+      }""", options = options)
+    }
+  }
+
+  @Test
+  def testDefaultNoAction(): Unit = {
+    check("Nil == None", None, List("config:testprops/defaultnoaction.properties"))
+  }
+
+  @Test
+  def testDefaultError(): Unit = {
+    check("Nil == None", Some("error: Comparing with =="), List("config:testprops/defaulterror.properties"))
   }
 }