Rider: Solution was not specified for the project 'light_temp' Follow

I'm trying to run a test for my Rider plugin, however, the test errors out.

Here is the test:

class MyTest : LightPlatformCodeInsightFixtureTestCase() {

  fun testThatNeverRuns() {}

}

Here are the errors I get:

CompositeException (2 nested):
------------------------------
[0]: Solution was not specified for the project 'light_temp'
Please fire a bug on 'https://youtrack.jetbrains.com/issues/RIDER', copy technical details and attach them to the issue

=== Technical Details===
Project was created from: 
at com.intellij.util.ExceptionUtil.currentStackTrace(ExceptionUtil.java:53)
at com.intellij.psi.impl.DebugUtil.currentStackTrace(DebugUtil.java:485)
at com.intellij.openapi.project.impl.ProjectImpl.<init>(ProjectImpl.java:73)
at com.intellij.openapi.project.impl.ProjectManagerImpl.createProject(ProjectManagerImpl.java:300)
at com.intellij.openapi.project.impl.ProjectManagerImpl.newProject(ProjectManagerImpl.java:194)
at com.intellij.testFramework.PlatformTestCase.createProject(PlatformTestCase.java:275)
at com.intellij.testFramework.PlatformTestCase.createProject(PlatformTestCase.java:266)
at com.intellij.testFramework.LightPlatformTestCase.initProject(LightPlatformTestCase.java:225)
at com.intellij.testFramework.LightPlatformTestCase.doSetup(LightPlatformTestCase.java:293)
at com.intellij.testFramework.fixtures.impl.LightIdeaTestFixtureImpl.setUp(LightIdeaTestFixtureImpl.java:36)
at com.intellij.testFramework.fixtures.impl.CodeInsightTestFixtureImpl.lambda$setUp$21(CodeInsightTestFixtureImpl.java:1067)
at com.intellij.testFramework.EdtTestUtil$Companion$runInEdtAndWait$1.invoke(EdtTestUtil.kt:19)
at com.intellij.testFramework.EdtTestUtil$Companion$runInEdtAndWait$1.invoke(EdtTestUtil.kt:14)
at com.intellij.testFramework.EdtTestUtilKt.runInEdtAndWait(EdtTestUtil.kt:55)
at com.intellij.testFramework.EdtTestUtil$Companion.runInEdtAndWait(EdtTestUtil.kt:19)
at com.intellij.testFramework.EdtTestUtil.runInEdtAndWait(EdtTestUtil.kt)
at com.intellij.testFramework.fixtures.impl.CodeInsightTestFixtureImpl.setUp(CodeInsightTestFixtureImpl.java:1066)
at com.intellij.testFramework.fixtures.LightPlatformCodeInsightFixtureTestCase.setUp(LightPlatformCodeInsightFixtureTestCase.java:42)
at com.intellij.testFramework.UsefulTestCase.defaultRunBare(UsefulTestCase.java:377)
at com.intellij.testFramework.EdtTestUtil$Companion$runInEdtAndWait$1.invoke(EdtTestUtil.kt:19)
at com.intellij.testFramework.EdtTestUtil$Companion$runInEdtAndWait$1.invoke(EdtTestUtil.kt:14)
at com.intellij.testFramework.EdtTestUtilKt$runInEdtAndWait$2.run(EdtTestUtil.kt:59)
at java.desktop/java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:303)
at java.desktop/java.awt.EventQueue.dispatchEventImpl(EventQueue.java:770)
at java.desktop/java.awt.EventQueue$4.run(EventQueue.java:721)
at java.desktop/java.awt.EventQueue$4.run(EventQueue.java:715)
at java.base/java.security.AccessController.doPrivileged(Native Method)
at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:85)
at java.desktop/java.awt.EventQueue.dispatchEvent(EventQueue.java:740)
at com.intellij.ide.IdeEventQueue.dispatchEvent(IdeEventQueue.java:342)
at java.desktop/java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:203)
at java.desktop/java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:124)
at java.desktop/java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:113)
at java.desktop/java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:109)
at java.desktop/java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
at java.desktop/java.awt.EventDispatchThread.run(EventDispatchThread.java:90)

[1]: setUp() has not been called
------------------------------

Here is the Gradle settings:

intellij {
  type = 'RD'
  plugins = [ 'rider-plugins-appender' ]
  pluginName = 'theplugin'
  version = '2018.3.4'
  downloadSources = false
  instrumentCode = false
}

If I switch the type to 'IC' in the settings above (with some other small necessary changes like dropping the 'rider-plugins-appender'), this problem disappears. Could I be missing Rider specific settings?