when:
        def versionMetadata = locator.getVisualStudioInstalls()

        then:
        versionMetadata != null
        versionMetadata.size() == 0
    }

    def "returns empty list when vswhere cannot be found"() {
        given:
        vswhereNotFound()

        when:
        def versionMetadata = locator.getVisualStudioInstalls()

        then:
        versionMetadata != null

        when:
        VisualStudioInstallCandidate metadata = determiner.getVisualStudioMetadataFromInstallDir(dir1)

        then:
        1 * commandLineLocator.getVisualStudioInstalls() >> vswhereInstalls
        0 * windowsRegistryLocator.getVisualStudioInstalls()

        and:
        metadata.version == VersionNumber.parse("15.3.26730.16")
        metadata.installDir == dir1

        def dir1 = vsDir("vs1")
        def dir2 = vsDir("vs2")

        given:
        1 * commandLineLocator.getVisualStudioInstalls() >> []
        1 * windowsRegistryLocator.getVisualStudioInstalls() >> { [legacyVsInstall(dir1, "11.0"), legacyVsInstall(dir2, "12.0")] }
        0 * systemPathLocator.getVisualStudioInstalls()

        when:
        def result = visualStudioLocator.locateComponent(null)

        then:

        def vsDir = tmpDir.createDir("vs")
        def compiler = vsDir.file("cl.exe")

        when:
        List<VisualStudioInstallCandidate> metadata = locator.getVisualStudioInstalls()

        then:
        1 * os.findInPath("cl.exe") >> compiler
        1 * versionDeterminer.getVisualStudioMetadataFromCompiler(compiler) >> vsMetadata(vsDir, "15.0")

        and:

        def dir2 = tmpDir.createDir("Visual Studio 12.0")
        def dir3 = tmpDir.createDir("Visual Studio 11.0")

        when:
        List<VisualStudioInstallCandidate> metadata = locator.getVisualStudioInstalls()

        then:
        switch(foundIn) {
            case SOFTWARE_KEY:
                1 * windowsRegistry.getValueNames(_, SOFTWARE_KEY) >> ["14.0", "12.0", "11.0" ]

        if (installs.size() > 0) {
            VisualStudioInstallCandidate install = findMetadataForInstallDir(spec, installs);
            if (install != null) {
                return install;
            }
        } else {
            installs = windowsRegistryLocator.getVisualStudioInstalls();

import javax.annotation.Nonnull;
import java.util.List;

public interface VisualStudioVersionLocator {
    @Nonnull
    List<VisualStudioInstallCandidate> getVisualStudioInstalls();

    String getSource();

    private final List<VisualStudioInstallCandidate> installs = new ArrayList<>();
    private boolean initialized;

    @Nonnull
    @Override
    public List<VisualStudioInstallCandidate> getVisualStudioInstalls() {
        if (!initialized) {
            installs.addAll(locateInstalls());
            initialized = true;
        }

        return installs;
    }

        this.os = os;
        this.versionDeterminer = versionDeterminer;
    }

    @Nonnull
    @Override
    public List<VisualStudioInstallCandidate> getVisualStudioInstalls() {
        List<VisualStudioInstallCandidate> installs = new ArrayList<>();

        File compilerInPath = os.findInPath(LEGACY_COMPILER_FILENAME);
        if (compilerInPath == null) {

            initialised = true;
        }
    }

    private void locateInstallsWith(VisualStudioVersionLocator versionLocator) {
        List<VisualStudioInstallCandidate> installs = versionLocator.getVisualStudioInstalls();

        for (VisualStudioInstallCandidate install : installs) {
            addInstallIfValid(install, versionLocator.getSource());
        }
    }