test: Only register SoundSourceProviders when actually necessary

This allows tests to inherit from MixxxTest and still register
SoundSourceProviders themselves, e.g. by instantiating CoreServices.
It also reduces log spam caused by the sound source provider
registration.

src/test/librarytest.h

@@ -7,10 +7,11 @@
 #include "library/trackcollection.h"
 #include "library/trackcollectionmanager.h"
 #include "test/mixxxdbtest.h"
+#include "test/soundsourcemixin.h"
 #include "util/db/dbconnectionpooled.h"
 #include "util/db/dbconnectionpooler.h"
 
-class LibraryTest : public MixxxDbTest {
+class LibraryTest : public MixxxDbTest, SoundSourceMixin {
   protected:
     LibraryTest();
     ~LibraryTest() override = default;

src/test/mixxxtest.cpp

@@ -4,7 +4,6 @@
 
 #include "control/control.h"
 #include "library/coverartutils.h"
-#include "sources/soundsourceproxy.h"
 #include "util/cmdlineargs.h"
 #include "util/logging.h"
 
@@ -45,11 +44,6 @@ MixxxTest::ApplicationScope::ApplicationScope(int& argc, char** argv) {
 
     DEBUG_ASSERT(s_pApplication.isNull());
     s_pApplication.reset(new MixxxApplication(argc, argv));
-
-    const bool providersRegistered =
-            SoundSourceProxy::registerProviders();
-    Q_UNUSED(providersRegistered);
-    DEBUG_ASSERT(providersRegistered);
 }
 
 MixxxTest::ApplicationScope::~ApplicationScope() {

src/test/signalpathtest.h

@@ -21,6 +21,7 @@
 #include "mixer/sampler.h"
 #include "preferences/usersettings.h"
 #include "test/mixxxtest.h"
+#include "test/soundsourcemixin.h"
 #include "track/track.h"
 #include "util/defs.h"
 #include "util/memory.h"
@@ -55,7 +56,7 @@ class TestEngineMaster : public EngineMaster {
     }
 };
 
-class BaseSignalPathTest : public MixxxTest {
+class BaseSignalPathTest : public MixxxTest, SoundSourceMixin {
   protected:
     BaseSignalPathTest() {
         m_pGuiTick = std::make_unique<GuiTick>();

src/test/soundproxy_test.cpp

@@ -4,6 +4,7 @@
 #include "sources/audiosourcestereoproxy.h"
 #include "sources/soundsourceproxy.h"
 #include "test/mixxxtest.h"
+#include "test/soundsourcemixin.h"
 #include "track/track.h"
 #include "track/trackmetadata.h"
 #include "util/samplebuffer.h"
@@ -35,7 +36,7 @@ const CSAMPLE kMaxDecodingError = 0.01f;
 
 } // anonymous namespace
 
-class SoundSourceProxyTest : public MixxxTest {
+class SoundSourceProxyTest : public MixxxTest, SoundSourceMixin {
   protected:
     static QStringList getFileNameSuffixes() {
         QStringList availableFileNameSuffixes;

src/test/soundsourcemixin.h

@@ -0,0 +1,12 @@
+#pragma once
+#include "sources/soundsourceproxy.h"
+
+class SoundSourceMixin {
+  protected:
+    SoundSourceMixin() {
+        const bool providersRegistered =
+                SoundSourceProxy::registerProviders();
+        Q_UNUSED(providersRegistered);
+        DEBUG_ASSERT(providersRegistered);
+    }
+};

src/test/trackupdate_test.cpp

@@ -3,6 +3,7 @@
 #include "library/coverart.h"
 #include "sources/soundsourceproxy.h"
 #include "test/mixxxtest.h"
+#include "test/soundsourcemixin.h"
 #include "track/track.h"
 
 namespace {
@@ -12,7 +13,7 @@ const QDir kTestDir(QDir::current().absoluteFilePath("src/test/id3-test-data"));
 } // anonymous namespace
 
 // Test for updating track metadata and cover art from files.
-class TrackUpdateTest: public MixxxTest {
+class TrackUpdateTest : public MixxxTest, SoundSourceMixin {
   protected:
     static bool hasTrackMetadata(const TrackPointer& pTrack) {
         return !pTrack->getArtist().isEmpty();