Test for haskell#960

Added a test for the problem where a library package has a testsuite
that depends on a packge that depends on it. We should be able to handle
this by having separate build plans for the library and its testsuite.

The ticket for separate build plans is haskell#1575

cabal-install/tests/IntegrationTests/circular-testsuite/should_run/a/A.hs

@@ -0,0 +1,4 @@
+module A where
+
+a :: ()
+a = ()

cabal-install/tests/IntegrationTests/circular-testsuite/should_run/a/Setup.hs

@@ -0,0 +1,2 @@
+import Distribution.Simple
+main = defaultMain

cabal-install/tests/IntegrationTests/circular-testsuite/should_run/a/a.cabal

@@ -0,0 +1,18 @@
+name:                a
+version:             0.1.0.0
+license:             BSD3
+license-file:        LICENSE
+author:              Echo Nolan
+category:            TestSuite
+build-type:          Simple
+cabal-version:       >=1.10
+
+library
+  exposed-modules:     A
+  build-depends:       base
+  default-language:    Haskell2010
+
+Test-Suite tests
+  type: exitcode-stdio-1.0
+  main-is: test.hs
+  build-depends: b

cabal-install/tests/IntegrationTests/circular-testsuite/should_run/b/B.hs

@@ -0,0 +1,4 @@
+module B where
+
+b :: ()
+b = ()

cabal-install/tests/IntegrationTests/circular-testsuite/should_run/b/Setup.hs

@@ -0,0 +1,2 @@
+import Distribution.Simple
+main = defaultMain

cabal-install/tests/IntegrationTests/circular-testsuite/should_run/b/b.cabal

@@ -0,0 +1,13 @@
+name:                b
+version:             0.1.0.0
+license:             BSD3
+license-file:        LICENSE
+author:              Echo Nolan
+category:            TestSuite
+build-type:          Simple
+cabal-version:       >=1.10
+
+library
+  exposed-modules:     B
+  build-depends:       base, a
+  default-language:    Haskell2010

cabal-install/tests/IntegrationTests/circular-testsuite/should_run/testsuite-dependencies-are-independent.sh

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+# Helper to run Cabal
+cabal() {
+    $CABAL $CABAL_ARGS "$@"
+}
+
+die() {
+    echo "die: $@"
+    exit 1
+}
+
+cabal sandbox init
+cabal sandbox add-source a
+cabal sandbox add-source b
+cabal install --enable-tests a