diff --git a/src/test/groovy/net/fabricmc/loom/test/integration/CustomManifestTest.groovy b/src/test/groovy/net/fabricmc/loom/test/integration/CustomManifestTest.groovy
new file mode 100644
index 0000000..aa849c1
--- /dev/null
+++ b/src/test/groovy/net/fabricmc/loom/test/integration/CustomManifestTest.groovy
@@ -0,0 +1,65 @@
+/*
+ * This file is part of fabric-loom, licensed under the MIT License (MIT).
+ *
+ * Copyright (c) 2021 FabricMC
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+package net.fabricmc.loom.test.integration
+
+import net.fabricmc.loom.test.util.ProjectTestTrait
+import spock.lang.Specification
+import spock.lang.Unroll
+
+import static org.gradle.testkit.runner.TaskOutcome.SUCCESS
+
+class CustomManifestTest extends Specification implements ProjectTestTrait {
+    @Override
+    String name() {
+        "minimalBase"
+    }
+
+    @Override
+    def filesReady() {
+        buildGradle() << '''
+            loom {
+                customManifest = "https://maven.fabricmc.net/net/minecraft/1_18_experimental-snapshot-1.json"
+            }
+
+            dependencies {
+                minecraft "com.mojang:minecraft:1.18_experimental-snapshot-1"
+                mappings "net.fabricmc:yarn:1.18_experimental-snapshot-1+build.2:v2"
+                modImplementation "net.fabricmc:fabric-loader:0.11.6"
+            }
+        '''
+    }
+
+    @Unroll
+    def "customManifest (gradle #gradle)"() {
+        when:
+            def result = create("build", gradle)
+        then:
+            result.task(":build").outcome == SUCCESS
+        where:
+            gradle              | _
+            DEFAULT_GRADLE      | _
+            PRE_RELEASE_GRADLE  | _
+    }
+}
diff --git a/src/test/groovy/net/fabricmc/loom/test/util/ProjectTestTrait.groovy b/src/test/groovy/net/fabricmc/loom/test/util/ProjectTestTrait.groovy
index 7097681..c9a5eeb 100644
--- a/src/test/groovy/net/fabricmc/loom/test/util/ProjectTestTrait.groovy
+++ b/src/test/groovy/net/fabricmc/loom/test/util/ProjectTestTrait.groovy
@@ -79,9 +79,17 @@ trait ProjectTestTrait {
 		gradleHome.deleteDir()
 	}
 
+	File buildGradle() {
+		return new File(testProjectDir, "build.gradle")
+	}
+
+	def filesReady() {
+	}
+
 	BuildResult create(String task, String gradleVersion = DEFAULT_GRADLE) {
 		System.setProperty("fabric.loom.test", "true")
 		copyInputFiles()
+		filesReady()
 
 		GradleRunner.create()
 			.withProjectDir(testProjectDir)
diff --git a/src/test/resources/projects/minimalBase/build.gradle b/src/test/resources/projects/minimalBase/build.gradle
new file mode 100644
index 0000000..8fbea23
--- /dev/null
+++ b/src/test/resources/projects/minimalBase/build.gradle
@@ -0,0 +1,10 @@
+// This is used by a range of tests that append to this file before running the gradle tasks.
+// Can be used for tests that require minimal custom setup
+plugins {
+	id 'fabric-loom'
+	id 'maven-publish'
+}
+
+archivesBaseName = "fabric-example-mod"
+version = "1.0.0"
+group = "com.example"
\ No newline at end of file