diff --git a/src/main/scala/software/purpledragon/sbt/lock/DependencyLockPlugin.scala b/src/main/scala/software/purpledragon/sbt/lock/DependencyLockPlugin.scala
index 289d170..2852fd8 100644
--- a/src/main/scala/software/purpledragon/sbt/lock/DependencyLockPlugin.scala
+++ b/src/main/scala/software/purpledragon/sbt/lock/DependencyLockPlugin.scala
@@ -18,6 +18,8 @@ package software.purpledragon.sbt.lock
 
 import sbt.Keys._
 import sbt._
+import sbt.internal.util.ManagedLogger
+import software.purpledragon.sbt.lock.DependencyLockUpdateMode._
 import software.purpledragon.sbt.lock.model.{DependencyLockFile, LockFileMatches}
 
 object DependencyLockPlugin extends AutoPlugin {
@@ -29,12 +31,20 @@ object DependencyLockPlugin extends AutoPlugin {
     val dependencyLockRead = taskKey[Option[DependencyLockFile]]("read dependencies from lock file")
 
     val dependencyLockCheck = taskKey[Unit]("check if dependency lock is up to date")
+
+    val DependencyLockUpdateMode: software.purpledragon.sbt.lock.DependencyLockUpdateMode.type =
+      software.purpledragon.sbt.lock.DependencyLockUpdateMode
+    val dependencyLockAutoCheck = settingKey[DependencyLockUpdateMode]("automatically check lock file after update")
   }
 
   import autoImport._
 
+  // task names to skip auto-check if we're inside of
+  private val PluginTasks = Seq("dependencyLockWrite", "dependencyLockCheck", "dependencyLockRead")
+
   override def projectSettings: Seq[Def.Setting[_]] = Seq(
     dependencyLockFile := baseDirectory.value / "build.sbt.lock",
+    dependencyLockAutoCheck := DependencyLockUpdateMode.WarnOnError,
     dependencyLockWrite := {
       val dest = dependencyLockFile.value
       val updateReport = update.value
@@ -49,8 +59,8 @@ object DependencyLockPlugin extends AutoPlugin {
       deps
     },
     dependencyLockCheck := {
-      val logger = streams.value.log
-      val updateReport = update.value
+      val logger: ManagedLogger = streams.value.log
+      val updateReport: UpdateReport = update.value
 
       val currentFile = dependencyLockRead.value.getOrElse(sys.error("no lock file"))
       val updatedFile = DependencyUtils.resolve(updateReport, thisProject.value.configurations.map(_.toConfigRef))
@@ -63,6 +73,47 @@ object DependencyLockPlugin extends AutoPlugin {
         logger.warn(changes.toShortReport)
         sys.error(changes.toLongReport)
       }
-    }
+    },
+    update := Def.taskDyn {
+      val report = update.value
+      val logger = streams.value.log
+
+
+      // check to see if the current command/task is one of our internal ones
+      val skipCheck = state.value.currentCommand.map(_.commandLine).exists(PluginTasks.contains)
+      val checkMode = dependencyLockAutoCheck.value
+
+      if (checkMode != DependencyLockUpdateMode.CheckDisabled && !skipCheck) {
+        logger.debug("Automatically checking lockfile")
+
+        dependencyLockRead.value match {
+          case Some(currentFile) =>
+            val updatedFile = DependencyUtils.resolve(report, thisProject.value.configurations.map(_.toConfigRef))
+
+            val changes = currentFile.findChanges(updatedFile)
+
+            (changes, checkMode) match {
+              case (LockFileMatches, _) =>
+              // check passed
+              case (_, WarnOnError) =>
+                logger.warn("Dependency lock file is outdated - please run `dependencyLockCheck` for details")
+              case (_, FailOnError) =>
+                logger.error("Dependency lock file is outdated")
+                sys.error(changes.toLongReport)
+
+              case _ =>
+              // scenario shouldn't happen - failed check, but we're not checking...
+            }
+
+          case None =>
+            logger.warn("no lockfile found - please run dependencyLockWrite")
+        }
+      }
+
+      // return the original report
+      Def.task {
+        report
+      }
+    }.value
   )
 }
diff --git a/src/main/scala/software/purpledragon/sbt/lock/DependencyLockUpdateMode.scala b/src/main/scala/software/purpledragon/sbt/lock/DependencyLockUpdateMode.scala
new file mode 100644
index 0000000..3922eb6
--- /dev/null
+++ b/src/main/scala/software/purpledragon/sbt/lock/DependencyLockUpdateMode.scala
@@ -0,0 +1,23 @@
+/*
+ * Copyright 2019 Michael Stringer
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package software.purpledragon.sbt.lock
+
+object DependencyLockUpdateMode extends Enumeration {
+  type DependencyLockUpdateMode = Value
+
+  val CheckDisabled, WarnOnError, FailOnError = Value
+}
diff --git a/src/sbt-test/sbt-dependency-lock/check-fail/build.sbt b/src/sbt-test/dependencyLockCheck/fail-differences/build.sbt
similarity index 100%
rename from src/sbt-test/sbt-dependency-lock/check-fail/build.sbt
rename to src/sbt-test/dependencyLockCheck/fail-differences/build.sbt
diff --git a/src/sbt-test/sbt-dependency-lock/check-fail/build.sbt.lock b/src/sbt-test/dependencyLockCheck/fail-differences/build.sbt.lock
similarity index 100%
rename from src/sbt-test/sbt-dependency-lock/check-fail/build.sbt.lock
rename to src/sbt-test/dependencyLockCheck/fail-differences/build.sbt.lock
diff --git a/src/sbt-test/sbt-dependency-lock/check-different-order/project/plugins.sbt b/src/sbt-test/dependencyLockCheck/fail-differences/project/plugins.sbt
similarity index 100%
rename from src/sbt-test/sbt-dependency-lock/check-different-order/project/plugins.sbt
rename to src/sbt-test/dependencyLockCheck/fail-differences/project/plugins.sbt
diff --git a/src/sbt-test/sbt-dependency-lock/check-fail/test b/src/sbt-test/dependencyLockCheck/fail-differences/test
similarity index 100%
rename from src/sbt-test/sbt-dependency-lock/check-fail/test
rename to src/sbt-test/dependencyLockCheck/fail-differences/test
diff --git a/src/sbt-test/sbt-dependency-lock/check-different-order/build.sbt b/src/sbt-test/dependencyLockCheck/fail-missing-file/build.sbt
similarity index 100%
rename from src/sbt-test/sbt-dependency-lock/check-different-order/build.sbt
rename to src/sbt-test/dependencyLockCheck/fail-missing-file/build.sbt
diff --git a/src/sbt-test/sbt-dependency-lock/check-fail/project/plugins.sbt b/src/sbt-test/dependencyLockCheck/fail-missing-file/project/plugins.sbt
similarity index 100%
rename from src/sbt-test/sbt-dependency-lock/check-fail/project/plugins.sbt
rename to src/sbt-test/dependencyLockCheck/fail-missing-file/project/plugins.sbt
diff --git a/src/sbt-test/sbt-dependency-lock/check-missing/test b/src/sbt-test/dependencyLockCheck/fail-missing-file/test
similarity index 100%
rename from src/sbt-test/sbt-dependency-lock/check-missing/test
rename to src/sbt-test/dependencyLockCheck/fail-missing-file/test
diff --git a/src/sbt-test/sbt-dependency-lock/check-missing/build.sbt b/src/sbt-test/dependencyLockCheck/pass-different-order/build.sbt
similarity index 100%
rename from src/sbt-test/sbt-dependency-lock/check-missing/build.sbt
rename to src/sbt-test/dependencyLockCheck/pass-different-order/build.sbt
diff --git a/src/sbt-test/sbt-dependency-lock/check-different-order/build.sbt.lock b/src/sbt-test/dependencyLockCheck/pass-different-order/build.sbt.lock
similarity index 100%
rename from src/sbt-test/sbt-dependency-lock/check-different-order/build.sbt.lock
rename to src/sbt-test/dependencyLockCheck/pass-different-order/build.sbt.lock
diff --git a/src/sbt-test/sbt-dependency-lock/check-missing/project/plugins.sbt b/src/sbt-test/dependencyLockCheck/pass-different-order/project/plugins.sbt
similarity index 100%
rename from src/sbt-test/sbt-dependency-lock/check-missing/project/plugins.sbt
rename to src/sbt-test/dependencyLockCheck/pass-different-order/project/plugins.sbt
diff --git a/src/sbt-test/sbt-dependency-lock/check-different-order/test b/src/sbt-test/dependencyLockCheck/pass-different-order/test
similarity index 100%
rename from src/sbt-test/sbt-dependency-lock/check-different-order/test
rename to src/sbt-test/dependencyLockCheck/pass-different-order/test
diff --git a/src/sbt-test/sbt-dependency-lock/check-pass/build.sbt b/src/sbt-test/dependencyLockCheck/pass/build.sbt
similarity index 100%
rename from src/sbt-test/sbt-dependency-lock/check-pass/build.sbt
rename to src/sbt-test/dependencyLockCheck/pass/build.sbt
diff --git a/src/sbt-test/sbt-dependency-lock/check-pass/build.sbt.lock b/src/sbt-test/dependencyLockCheck/pass/build.sbt.lock
similarity index 100%
rename from src/sbt-test/sbt-dependency-lock/check-pass/build.sbt.lock
rename to src/sbt-test/dependencyLockCheck/pass/build.sbt.lock
diff --git a/src/sbt-test/sbt-dependency-lock/check-pass/project/plugins.sbt b/src/sbt-test/dependencyLockCheck/pass/project/plugins.sbt
similarity index 100%
rename from src/sbt-test/sbt-dependency-lock/check-pass/project/plugins.sbt
rename to src/sbt-test/dependencyLockCheck/pass/project/plugins.sbt
diff --git a/src/sbt-test/sbt-dependency-lock/check-pass/test b/src/sbt-test/dependencyLockCheck/pass/test
similarity index 100%
rename from src/sbt-test/sbt-dependency-lock/check-pass/test
rename to src/sbt-test/dependencyLockCheck/pass/test
diff --git a/src/sbt-test/update/disabled-differences/build.sbt b/src/sbt-test/update/disabled-differences/build.sbt
new file mode 100644
index 0000000..5abbcb3
--- /dev/null
+++ b/src/sbt-test/update/disabled-differences/build.sbt
@@ -0,0 +1,9 @@
+scalaVersion := "2.12.10"
+
+libraryDependencies ++= Seq(
+  "org.apache.commons"  %  "commons-lang3"  % "3.9",
+  // lock file has 3.0.8
+  "org.scalatest"       %% "scalatest"      % "3.0.7"   % Test,
+)
+
+dependencyLockAutoCheck := DependencyLockUpdateMode.CheckDisabled
\ No newline at end of file
diff --git a/src/sbt-test/update/disabled-differences/build.sbt.lock b/src/sbt-test/update/disabled-differences/build.sbt.lock
new file mode 100644
index 0000000..cae2104
--- /dev/null
+++ b/src/sbt-test/update/disabled-differences/build.sbt.lock
@@ -0,0 +1,101 @@
+{
+  "lockVersion" : 1,
+  "timestamp" : "2019-11-21T18:42:01.200Z",
+  "configurations" : [
+    "compile",
+    "optional",
+    "provided",
+    "runtime",
+    "test"
+  ],
+  "dependencies" : [
+    {
+      "org" : "org.apache.commons",
+      "name" : "commons-lang3",
+      "version" : "3.9",
+      "artifacts" : [
+        {
+          "name" : "commons-lang3.jar",
+          "hash" : "sha1:0122c7cee69b53ed4a7681c03d4ee4c0e2765da5"
+        }
+      ],
+      "configurations" : [
+        "test",
+        "compile",
+        "runtime"
+      ]
+    },
+    {
+      "org" : "org.scala-lang",
+      "name" : "scala-library",
+      "version" : "2.12.10",
+      "artifacts" : [
+        {
+          "name" : "scala-library.jar",
+          "hash" : "sha1:3509860bc2e5b3da001ed45aca94ffbe5694dbda"
+        }
+      ],
+      "configurations" : [
+        "test",
+        "compile",
+        "runtime"
+      ]
+    },
+    {
+      "org" : "org.scala-lang",
+      "name" : "scala-reflect",
+      "version" : "2.12.10",
+      "artifacts" : [
+        {
+          "name" : "scala-reflect.jar",
+          "hash" : "sha1:14cb7beb516cd8e07716133668c427792122c926"
+        }
+      ],
+      "configurations" : [
+        "test"
+      ]
+    },
+    {
+      "org" : "org.scala-lang.modules",
+      "name" : "scala-xml_2.12",
+      "version" : "1.2.0",
+      "artifacts" : [
+        {
+          "name" : "scala-xml_2.12.jar",
+          "hash" : "sha1:5d38ac30beb8420dd395c0af447ba412158965e6"
+        }
+      ],
+      "configurations" : [
+        "test"
+      ]
+    },
+    {
+      "org" : "org.scalactic",
+      "name" : "scalactic_2.12",
+      "version" : "3.0.8",
+      "artifacts" : [
+        {
+          "name" : "scalactic_2.12.jar",
+          "hash" : "sha1:b50559dfc4a691c1089f9c8812e1d6fd17f80277"
+        }
+      ],
+      "configurations" : [
+        "test"
+      ]
+    },
+    {
+      "org" : "org.scalatest",
+      "name" : "scalatest_2.12",
+      "version" : "3.0.8",
+      "artifacts" : [
+        {
+          "name" : "scalatest_2.12.jar",
+          "hash" : "sha1:8493ffa579676977b810a7a9fdc23af9d3c8af7f"
+        }
+      ],
+      "configurations" : [
+        "test"
+      ]
+    }
+  ]
+}
\ No newline at end of file
diff --git a/src/sbt-test/update/disabled-differences/project/plugins.sbt b/src/sbt-test/update/disabled-differences/project/plugins.sbt
new file mode 100644
index 0000000..85547d6
--- /dev/null
+++ b/src/sbt-test/update/disabled-differences/project/plugins.sbt
@@ -0,0 +1,7 @@
+{
+  val pluginVersion = System.getProperty("plugin.version")
+  if (pluginVersion == null)
+    throw new RuntimeException("""|The system property 'plugin.version' is not defined.
+                                  |Specify this property using the scriptedLaunchOpts -D.""".stripMargin)
+  else addSbtPlugin("software.purpledragon" % "sbt-dependency-lock" % pluginVersion)
+}
diff --git a/src/sbt-test/update/disabled-differences/test b/src/sbt-test/update/disabled-differences/test
new file mode 100644
index 0000000..edf1fbd
--- /dev/null
+++ b/src/sbt-test/update/disabled-differences/test
@@ -0,0 +1 @@
+> update
\ No newline at end of file
diff --git a/src/sbt-test/update/disabled-same/build.sbt b/src/sbt-test/update/disabled-same/build.sbt
new file mode 100644
index 0000000..54d14d9
--- /dev/null
+++ b/src/sbt-test/update/disabled-same/build.sbt
@@ -0,0 +1,19 @@
+scalaVersion := "2.12.10"
+
+libraryDependencies ++= Seq(
+  "org.apache.commons"  %  "commons-lang3"  % "3.9",
+  "org.scalatest"       %% "scalatest"      % "3.0.8"   % Test,
+)
+
+dependencyLockAutoCheck := DependencyLockUpdateMode.CheckDisabled
+
+val checkLog = taskKey[Unit]("checks the contents of the log")
+
+checkLog := {
+  val lastLog = BuiltinCommands.lastLogFile(state.value).get
+  val last = IO.read(lastLog)
+
+  if (last.contains("Dependency lock file is outdated")) {
+    sys.error("check contained warning")
+  }
+}
\ No newline at end of file
diff --git a/src/sbt-test/update/disabled-same/build.sbt.lock b/src/sbt-test/update/disabled-same/build.sbt.lock
new file mode 100644
index 0000000..cae2104
--- /dev/null
+++ b/src/sbt-test/update/disabled-same/build.sbt.lock
@@ -0,0 +1,101 @@
+{
+  "lockVersion" : 1,
+  "timestamp" : "2019-11-21T18:42:01.200Z",
+  "configurations" : [
+    "compile",
+    "optional",
+    "provided",
+    "runtime",
+    "test"
+  ],
+  "dependencies" : [
+    {
+      "org" : "org.apache.commons",
+      "name" : "commons-lang3",
+      "version" : "3.9",
+      "artifacts" : [
+        {
+          "name" : "commons-lang3.jar",
+          "hash" : "sha1:0122c7cee69b53ed4a7681c03d4ee4c0e2765da5"
+        }
+      ],
+      "configurations" : [
+        "test",
+        "compile",
+        "runtime"
+      ]
+    },
+    {
+      "org" : "org.scala-lang",
+      "name" : "scala-library",
+      "version" : "2.12.10",
+      "artifacts" : [
+        {
+          "name" : "scala-library.jar",
+          "hash" : "sha1:3509860bc2e5b3da001ed45aca94ffbe5694dbda"
+        }
+      ],
+      "configurations" : [
+        "test",
+        "compile",
+        "runtime"
+      ]
+    },
+    {
+      "org" : "org.scala-lang",
+      "name" : "scala-reflect",
+      "version" : "2.12.10",
+      "artifacts" : [
+        {
+          "name" : "scala-reflect.jar",
+          "hash" : "sha1:14cb7beb516cd8e07716133668c427792122c926"
+        }
+      ],
+      "configurations" : [
+        "test"
+      ]
+    },
+    {
+      "org" : "org.scala-lang.modules",
+      "name" : "scala-xml_2.12",
+      "version" : "1.2.0",
+      "artifacts" : [
+        {
+          "name" : "scala-xml_2.12.jar",
+          "hash" : "sha1:5d38ac30beb8420dd395c0af447ba412158965e6"
+        }
+      ],
+      "configurations" : [
+        "test"
+      ]
+    },
+    {
+      "org" : "org.scalactic",
+      "name" : "scalactic_2.12",
+      "version" : "3.0.8",
+      "artifacts" : [
+        {
+          "name" : "scalactic_2.12.jar",
+          "hash" : "sha1:b50559dfc4a691c1089f9c8812e1d6fd17f80277"
+        }
+      ],
+      "configurations" : [
+        "test"
+      ]
+    },
+    {
+      "org" : "org.scalatest",
+      "name" : "scalatest_2.12",
+      "version" : "3.0.8",
+      "artifacts" : [
+        {
+          "name" : "scalatest_2.12.jar",
+          "hash" : "sha1:8493ffa579676977b810a7a9fdc23af9d3c8af7f"
+        }
+      ],
+      "configurations" : [
+        "test"
+      ]
+    }
+  ]
+}
\ No newline at end of file
diff --git a/src/sbt-test/update/disabled-same/project/plugins.sbt b/src/sbt-test/update/disabled-same/project/plugins.sbt
new file mode 100644
index 0000000..85547d6
--- /dev/null
+++ b/src/sbt-test/update/disabled-same/project/plugins.sbt
@@ -0,0 +1,7 @@
+{
+  val pluginVersion = System.getProperty("plugin.version")
+  if (pluginVersion == null)
+    throw new RuntimeException("""|The system property 'plugin.version' is not defined.
+                                  |Specify this property using the scriptedLaunchOpts -D.""".stripMargin)
+  else addSbtPlugin("software.purpledragon" % "sbt-dependency-lock" % pluginVersion)
+}
diff --git a/src/sbt-test/update/disabled-same/test b/src/sbt-test/update/disabled-same/test
new file mode 100644
index 0000000..e211012
--- /dev/null
+++ b/src/sbt-test/update/disabled-same/test
@@ -0,0 +1,2 @@
+> update
+> checkLog
diff --git a/src/sbt-test/update/fail-differences/build.sbt b/src/sbt-test/update/fail-differences/build.sbt
new file mode 100644
index 0000000..e0e9153
--- /dev/null
+++ b/src/sbt-test/update/fail-differences/build.sbt
@@ -0,0 +1,9 @@
+scalaVersion := "2.12.10"
+
+libraryDependencies ++= Seq(
+  "org.apache.commons"  %  "commons-lang3"  % "3.9",
+  // lock file has 3.0.8
+  "org.scalatest"       %% "scalatest"      % "3.0.7"   % Test,
+)
+
+dependencyLockAutoCheck := DependencyLockUpdateMode.FailOnError
\ No newline at end of file
diff --git a/src/sbt-test/update/fail-differences/build.sbt.lock b/src/sbt-test/update/fail-differences/build.sbt.lock
new file mode 100644
index 0000000..cae2104
--- /dev/null
+++ b/src/sbt-test/update/fail-differences/build.sbt.lock
@@ -0,0 +1,101 @@
+{
+  "lockVersion" : 1,
+  "timestamp" : "2019-11-21T18:42:01.200Z",
+  "configurations" : [
+    "compile",
+    "optional",
+    "provided",
+    "runtime",
+    "test"
+  ],
+  "dependencies" : [
+    {
+      "org" : "org.apache.commons",
+      "name" : "commons-lang3",
+      "version" : "3.9",
+      "artifacts" : [
+        {
+          "name" : "commons-lang3.jar",
+          "hash" : "sha1:0122c7cee69b53ed4a7681c03d4ee4c0e2765da5"
+        }
+      ],
+      "configurations" : [
+        "test",
+        "compile",
+        "runtime"
+      ]
+    },
+    {
+      "org" : "org.scala-lang",
+      "name" : "scala-library",
+      "version" : "2.12.10",
+      "artifacts" : [
+        {
+          "name" : "scala-library.jar",
+          "hash" : "sha1:3509860bc2e5b3da001ed45aca94ffbe5694dbda"
+        }
+      ],
+      "configurations" : [
+        "test",
+        "compile",
+        "runtime"
+      ]
+    },
+    {
+      "org" : "org.scala-lang",
+      "name" : "scala-reflect",
+      "version" : "2.12.10",
+      "artifacts" : [
+        {
+          "name" : "scala-reflect.jar",
+          "hash" : "sha1:14cb7beb516cd8e07716133668c427792122c926"
+        }
+      ],
+      "configurations" : [
+        "test"
+      ]
+    },
+    {
+      "org" : "org.scala-lang.modules",
+      "name" : "scala-xml_2.12",
+      "version" : "1.2.0",
+      "artifacts" : [
+        {
+          "name" : "scala-xml_2.12.jar",
+          "hash" : "sha1:5d38ac30beb8420dd395c0af447ba412158965e6"
+        }
+      ],
+      "configurations" : [
+        "test"
+      ]
+    },
+    {
+      "org" : "org.scalactic",
+      "name" : "scalactic_2.12",
+      "version" : "3.0.8",
+      "artifacts" : [
+        {
+          "name" : "scalactic_2.12.jar",
+          "hash" : "sha1:b50559dfc4a691c1089f9c8812e1d6fd17f80277"
+        }
+      ],
+      "configurations" : [
+        "test"
+      ]
+    },
+    {
+      "org" : "org.scalatest",
+      "name" : "scalatest_2.12",
+      "version" : "3.0.8",
+      "artifacts" : [
+        {
+          "name" : "scalatest_2.12.jar",
+          "hash" : "sha1:8493ffa579676977b810a7a9fdc23af9d3c8af7f"
+        }
+      ],
+      "configurations" : [
+        "test"
+      ]
+    }
+  ]
+}
\ No newline at end of file
diff --git a/src/sbt-test/update/fail-differences/project/plugins.sbt b/src/sbt-test/update/fail-differences/project/plugins.sbt
new file mode 100644
index 0000000..85547d6
--- /dev/null
+++ b/src/sbt-test/update/fail-differences/project/plugins.sbt
@@ -0,0 +1,7 @@
+{
+  val pluginVersion = System.getProperty("plugin.version")
+  if (pluginVersion == null)
+    throw new RuntimeException("""|The system property 'plugin.version' is not defined.
+                                  |Specify this property using the scriptedLaunchOpts -D.""".stripMargin)
+  else addSbtPlugin("software.purpledragon" % "sbt-dependency-lock" % pluginVersion)
+}
diff --git a/src/sbt-test/update/fail-differences/test b/src/sbt-test/update/fail-differences/test
new file mode 100644
index 0000000..85240ac
--- /dev/null
+++ b/src/sbt-test/update/fail-differences/test
@@ -0,0 +1 @@
+-> update
\ No newline at end of file
diff --git a/src/sbt-test/update/fail-same/build.sbt b/src/sbt-test/update/fail-same/build.sbt
new file mode 100644
index 0000000..9a22113
--- /dev/null
+++ b/src/sbt-test/update/fail-same/build.sbt
@@ -0,0 +1,19 @@
+scalaVersion := "2.12.10"
+
+libraryDependencies ++= Seq(
+  "org.apache.commons"  %  "commons-lang3"  % "3.9",
+  "org.scalatest"       %% "scalatest"      % "3.0.8"   % Test,
+)
+
+dependencyLockAutoCheck := DependencyLockUpdateMode.FailOnError
+
+val checkLog = taskKey[Unit]("checks the contents of the log")
+
+checkLog := {
+  val lastLog = BuiltinCommands.lastLogFile(state.value).get
+  val last = IO.read(lastLog)
+
+  if (last.contains("Dependency lock file is outdated")) {
+    sys.error("check contained warning")
+  }
+}
\ No newline at end of file
diff --git a/src/sbt-test/update/fail-same/build.sbt.lock b/src/sbt-test/update/fail-same/build.sbt.lock
new file mode 100644
index 0000000..cae2104
--- /dev/null
+++ b/src/sbt-test/update/fail-same/build.sbt.lock
@@ -0,0 +1,101 @@
+{
+  "lockVersion" : 1,
+  "timestamp" : "2019-11-21T18:42:01.200Z",
+  "configurations" : [
+    "compile",
+    "optional",
+    "provided",
+    "runtime",
+    "test"
+  ],
+  "dependencies" : [
+    {
+      "org" : "org.apache.commons",
+      "name" : "commons-lang3",
+      "version" : "3.9",
+      "artifacts" : [
+        {
+          "name" : "commons-lang3.jar",
+          "hash" : "sha1:0122c7cee69b53ed4a7681c03d4ee4c0e2765da5"
+        }
+      ],
+      "configurations" : [
+        "test",
+        "compile",
+        "runtime"
+      ]
+    },
+    {
+      "org" : "org.scala-lang",
+      "name" : "scala-library",
+      "version" : "2.12.10",
+      "artifacts" : [
+        {
+          "name" : "scala-library.jar",
+          "hash" : "sha1:3509860bc2e5b3da001ed45aca94ffbe5694dbda"
+        }
+      ],
+      "configurations" : [
+        "test",
+        "compile",
+        "runtime"
+      ]
+    },
+    {
+      "org" : "org.scala-lang",
+      "name" : "scala-reflect",
+      "version" : "2.12.10",
+      "artifacts" : [
+        {
+          "name" : "scala-reflect.jar",
+          "hash" : "sha1:14cb7beb516cd8e07716133668c427792122c926"
+        }
+      ],
+      "configurations" : [
+        "test"
+      ]
+    },
+    {
+      "org" : "org.scala-lang.modules",
+      "name" : "scala-xml_2.12",
+      "version" : "1.2.0",
+      "artifacts" : [
+        {
+          "name" : "scala-xml_2.12.jar",
+          "hash" : "sha1:5d38ac30beb8420dd395c0af447ba412158965e6"
+        }
+      ],
+      "configurations" : [
+        "test"
+      ]
+    },
+    {
+      "org" : "org.scalactic",
+      "name" : "scalactic_2.12",
+      "version" : "3.0.8",
+      "artifacts" : [
+        {
+          "name" : "scalactic_2.12.jar",
+          "hash" : "sha1:b50559dfc4a691c1089f9c8812e1d6fd17f80277"
+        }
+      ],
+      "configurations" : [
+        "test"
+      ]
+    },
+    {
+      "org" : "org.scalatest",
+      "name" : "scalatest_2.12",
+      "version" : "3.0.8",
+      "artifacts" : [
+        {
+          "name" : "scalatest_2.12.jar",
+          "hash" : "sha1:8493ffa579676977b810a7a9fdc23af9d3c8af7f"
+        }
+      ],
+      "configurations" : [
+        "test"
+      ]
+    }
+  ]
+}
\ No newline at end of file
diff --git a/src/sbt-test/update/fail-same/project/plugins.sbt b/src/sbt-test/update/fail-same/project/plugins.sbt
new file mode 100644
index 0000000..85547d6
--- /dev/null
+++ b/src/sbt-test/update/fail-same/project/plugins.sbt
@@ -0,0 +1,7 @@
+{
+  val pluginVersion = System.getProperty("plugin.version")
+  if (pluginVersion == null)
+    throw new RuntimeException("""|The system property 'plugin.version' is not defined.
+                                  |Specify this property using the scriptedLaunchOpts -D.""".stripMargin)
+  else addSbtPlugin("software.purpledragon" % "sbt-dependency-lock" % pluginVersion)
+}
diff --git a/src/sbt-test/update/fail-same/test b/src/sbt-test/update/fail-same/test
new file mode 100644
index 0000000..e211012
--- /dev/null
+++ b/src/sbt-test/update/fail-same/test
@@ -0,0 +1,2 @@
+> update
+> checkLog
diff --git a/src/sbt-test/update/warn-differences/build.sbt b/src/sbt-test/update/warn-differences/build.sbt
new file mode 100644
index 0000000..51af6ee
--- /dev/null
+++ b/src/sbt-test/update/warn-differences/build.sbt
@@ -0,0 +1,20 @@
+scalaVersion := "2.12.10"
+
+libraryDependencies ++= Seq(
+  "org.apache.commons"  %  "commons-lang3"  % "3.9",
+  // lock file has 3.0.8
+  "org.scalatest"       %% "scalatest"      % "3.0.7"   % Test,
+)
+
+dependencyLockAutoCheck := DependencyLockUpdateMode.WarnOnError
+
+val checkLog = taskKey[Unit]("checks the contents of the log")
+
+checkLog := {
+  val lastLog = BuiltinCommands.lastLogFile(state.value).get
+  val last = IO.read(lastLog)
+
+  if (!last.contains("Dependency lock file is outdated")) {
+    sys.error("check did not contain error")
+  }
+}
\ No newline at end of file
diff --git a/src/sbt-test/update/warn-differences/build.sbt.lock b/src/sbt-test/update/warn-differences/build.sbt.lock
new file mode 100644
index 0000000..cae2104
--- /dev/null
+++ b/src/sbt-test/update/warn-differences/build.sbt.lock
@@ -0,0 +1,101 @@
+{
+  "lockVersion" : 1,
+  "timestamp" : "2019-11-21T18:42:01.200Z",
+  "configurations" : [
+    "compile",
+    "optional",
+    "provided",
+    "runtime",
+    "test"
+  ],
+  "dependencies" : [
+    {
+      "org" : "org.apache.commons",
+      "name" : "commons-lang3",
+      "version" : "3.9",
+      "artifacts" : [
+        {
+          "name" : "commons-lang3.jar",
+          "hash" : "sha1:0122c7cee69b53ed4a7681c03d4ee4c0e2765da5"
+        }
+      ],
+      "configurations" : [
+        "test",
+        "compile",
+        "runtime"
+      ]
+    },
+    {
+      "org" : "org.scala-lang",
+      "name" : "scala-library",
+      "version" : "2.12.10",
+      "artifacts" : [
+        {
+          "name" : "scala-library.jar",
+          "hash" : "sha1:3509860bc2e5b3da001ed45aca94ffbe5694dbda"
+        }
+      ],
+      "configurations" : [
+        "test",
+        "compile",
+        "runtime"
+      ]
+    },
+    {
+      "org" : "org.scala-lang",
+      "name" : "scala-reflect",
+      "version" : "2.12.10",
+      "artifacts" : [
+        {
+          "name" : "scala-reflect.jar",
+          "hash" : "sha1:14cb7beb516cd8e07716133668c427792122c926"
+        }
+      ],
+      "configurations" : [
+        "test"
+      ]
+    },
+    {
+      "org" : "org.scala-lang.modules",
+      "name" : "scala-xml_2.12",
+      "version" : "1.2.0",
+      "artifacts" : [
+        {
+          "name" : "scala-xml_2.12.jar",
+          "hash" : "sha1:5d38ac30beb8420dd395c0af447ba412158965e6"
+        }
+      ],
+      "configurations" : [
+        "test"
+      ]
+    },
+    {
+      "org" : "org.scalactic",
+      "name" : "scalactic_2.12",
+      "version" : "3.0.8",
+      "artifacts" : [
+        {
+          "name" : "scalactic_2.12.jar",
+          "hash" : "sha1:b50559dfc4a691c1089f9c8812e1d6fd17f80277"
+        }
+      ],
+      "configurations" : [
+        "test"
+      ]
+    },
+    {
+      "org" : "org.scalatest",
+      "name" : "scalatest_2.12",
+      "version" : "3.0.8",
+      "artifacts" : [
+        {
+          "name" : "scalatest_2.12.jar",
+          "hash" : "sha1:8493ffa579676977b810a7a9fdc23af9d3c8af7f"
+        }
+      ],
+      "configurations" : [
+        "test"
+      ]
+    }
+  ]
+}
\ No newline at end of file
diff --git a/src/sbt-test/update/warn-differences/project/plugins.sbt b/src/sbt-test/update/warn-differences/project/plugins.sbt
new file mode 100644
index 0000000..85547d6
--- /dev/null
+++ b/src/sbt-test/update/warn-differences/project/plugins.sbt
@@ -0,0 +1,7 @@
+{
+  val pluginVersion = System.getProperty("plugin.version")
+  if (pluginVersion == null)
+    throw new RuntimeException("""|The system property 'plugin.version' is not defined.
+                                  |Specify this property using the scriptedLaunchOpts -D.""".stripMargin)
+  else addSbtPlugin("software.purpledragon" % "sbt-dependency-lock" % pluginVersion)
+}
diff --git a/src/sbt-test/update/warn-differences/test b/src/sbt-test/update/warn-differences/test
new file mode 100644
index 0000000..2019427
--- /dev/null
+++ b/src/sbt-test/update/warn-differences/test
@@ -0,0 +1,2 @@
+> update
+> checkLog
\ No newline at end of file
diff --git a/src/sbt-test/update/warn-same/build.sbt b/src/sbt-test/update/warn-same/build.sbt
new file mode 100644
index 0000000..38237b1
--- /dev/null
+++ b/src/sbt-test/update/warn-same/build.sbt
@@ -0,0 +1,19 @@
+scalaVersion := "2.12.10"
+
+libraryDependencies ++= Seq(
+  "org.apache.commons"  %  "commons-lang3"  % "3.9",
+  "org.scalatest"       %% "scalatest"      % "3.0.8"   % Test,
+)
+
+dependencyLockAutoCheck := DependencyLockUpdateMode.WarnOnError
+
+val checkLog = taskKey[Unit]("checks the contents of the log")
+
+checkLog := {
+  val lastLog = BuiltinCommands.lastLogFile(state.value).get
+  val last = IO.read(lastLog)
+
+  if (last.contains("Dependency lock file is outdated")) {
+    sys.error("check contained warning")
+  }
+}
\ No newline at end of file
diff --git a/src/sbt-test/update/warn-same/build.sbt.lock b/src/sbt-test/update/warn-same/build.sbt.lock
new file mode 100644
index 0000000..cae2104
--- /dev/null
+++ b/src/sbt-test/update/warn-same/build.sbt.lock
@@ -0,0 +1,101 @@
+{
+  "lockVersion" : 1,
+  "timestamp" : "2019-11-21T18:42:01.200Z",
+  "configurations" : [
+    "compile",
+    "optional",
+    "provided",
+    "runtime",
+    "test"
+  ],
+  "dependencies" : [
+    {
+      "org" : "org.apache.commons",
+      "name" : "commons-lang3",
+      "version" : "3.9",
+      "artifacts" : [
+        {
+          "name" : "commons-lang3.jar",
+          "hash" : "sha1:0122c7cee69b53ed4a7681c03d4ee4c0e2765da5"
+        }
+      ],
+      "configurations" : [
+        "test",
+        "compile",
+        "runtime"
+      ]
+    },
+    {
+      "org" : "org.scala-lang",
+      "name" : "scala-library",
+      "version" : "2.12.10",
+      "artifacts" : [
+        {
+          "name" : "scala-library.jar",
+          "hash" : "sha1:3509860bc2e5b3da001ed45aca94ffbe5694dbda"
+        }
+      ],
+      "configurations" : [
+        "test",
+        "compile",
+        "runtime"
+      ]
+    },
+    {
+      "org" : "org.scala-lang",
+      "name" : "scala-reflect",
+      "version" : "2.12.10",
+      "artifacts" : [
+        {
+          "name" : "scala-reflect.jar",
+          "hash" : "sha1:14cb7beb516cd8e07716133668c427792122c926"
+        }
+      ],
+      "configurations" : [
+        "test"
+      ]
+    },
+    {
+      "org" : "org.scala-lang.modules",
+      "name" : "scala-xml_2.12",
+      "version" : "1.2.0",
+      "artifacts" : [
+        {
+          "name" : "scala-xml_2.12.jar",
+          "hash" : "sha1:5d38ac30beb8420dd395c0af447ba412158965e6"
+        }
+      ],
+      "configurations" : [
+        "test"
+      ]
+    },
+    {
+      "org" : "org.scalactic",
+      "name" : "scalactic_2.12",
+      "version" : "3.0.8",
+      "artifacts" : [
+        {
+          "name" : "scalactic_2.12.jar",
+          "hash" : "sha1:b50559dfc4a691c1089f9c8812e1d6fd17f80277"
+        }
+      ],
+      "configurations" : [
+        "test"
+      ]
+    },
+    {
+      "org" : "org.scalatest",
+      "name" : "scalatest_2.12",
+      "version" : "3.0.8",
+      "artifacts" : [
+        {
+          "name" : "scalatest_2.12.jar",
+          "hash" : "sha1:8493ffa579676977b810a7a9fdc23af9d3c8af7f"
+        }
+      ],
+      "configurations" : [
+        "test"
+      ]
+    }
+  ]
+}
\ No newline at end of file
diff --git a/src/sbt-test/update/warn-same/project/plugins.sbt b/src/sbt-test/update/warn-same/project/plugins.sbt
new file mode 100644
index 0000000..85547d6
--- /dev/null
+++ b/src/sbt-test/update/warn-same/project/plugins.sbt
@@ -0,0 +1,7 @@
+{
+  val pluginVersion = System.getProperty("plugin.version")
+  if (pluginVersion == null)
+    throw new RuntimeException("""|The system property 'plugin.version' is not defined.
+                                  |Specify this property using the scriptedLaunchOpts -D.""".stripMargin)
+  else addSbtPlugin("software.purpledragon" % "sbt-dependency-lock" % pluginVersion)
+}
diff --git a/src/sbt-test/update/warn-same/test b/src/sbt-test/update/warn-same/test
new file mode 100644
index 0000000..e211012
--- /dev/null
+++ b/src/sbt-test/update/warn-same/test
@@ -0,0 +1,2 @@
+> update
+> checkLog