def lib = libs.foo
                assert lib instanceof Provider
                doLast {
                    def dep = lib.get()
                    assert dep instanceof MinimalExternalModuleDependency
                    assert dep.module.group == 'org.gradle.test'
                    assert dep.module.name == 'lib'
                    assert dep.versionConstraint.requiredVersion == '1.0'
                }

public operator fun DependencyAdder.invoke(dependency: Provider<out Dependency>): Unit defined in org.gradle.kotlin.dsl
public operator fun DependencyAdder.invoke(externalModule: ProviderConvertible<out MinimalExternalModuleDependency>): Unit defined in org.gradle.kotlin.dsl
```

To fix this, replace the reference to `project` with a call to `project()`:

```kotlin
testing {
  suites {