diff --git a/Makefile b/Makefile
index 1ae6bd9..1e285a6 100644
--- a/Makefile
+++ b/Makefile
@@ -2,6 +2,22 @@
 DESTDIR=/usr/local
 PREFIX=mbedtls_
 
+PROGRAMS_DIR=./programs
+TESTS_DIR=./tests
+
+# Check test environment. If ../library is available then Mbed TLS is used.
+# Otherwise Mbed OS environment is used.
+DIR_FOR_MBED_TLS_ENV=./library
+ifneq "$(wildcard $(DIR_FOR_MBED_TLS_ENV) )" ""
+	LIBRARY_DIR=./library
+	INCLUDE_DIR=./include
+	CONFIG_FILE=./include/mbedtls/config.h
+else
+	LIBRARY_DIR=./src
+	INCLUDE_DIR=./inc
+	CONFIG_FILE=./inc/mbedtls/test_config.h
+endif
+
 .SILENT:
 
 .PHONY: all no_test programs lib tests install uninstall clean test check covtest lcov apidoc apidoc_clean
@@ -12,26 +28,26 @@
 no_test: programs
 
 programs: lib
-	$(MAKE) -C programs
+	$(MAKE) -C $(PROGRAMS_DIR)
 
 lib:
-	$(MAKE) -C library
+	$(MAKE) -C $(LIBRARY_DIR)
 
 tests: lib
-	$(MAKE) -C tests
+	$(MAKE) -C $(TESTS_DIR)
 
 ifndef WINDOWS
 install: no_test
-	mkdir -p $(DESTDIR)/include/mbedtls
-	cp -rp include/mbedtls $(DESTDIR)/include
+	mkdir -p $(DESTDIR)/$(INCLUDE_DIR)/mbedtls
+	cp -rp $(INCLUDE_DIR)/mbedtls $(DESTDIR)/$(INCLUDE_DIR)
 
 	mkdir -p $(DESTDIR)/lib
-	cp -RP library/libmbedtls.*    $(DESTDIR)/lib
-	cp -RP library/libmbedx509.*   $(DESTDIR)/lib
-	cp -RP library/libmbedcrypto.* $(DESTDIR)/lib
+	cp -RP $(LIBRARY_DIR)/libmbedtls.*    $(DESTDIR)/lib
+	cp -RP $(LIBRARY_DIR)/libmbedx509.*   $(DESTDIR)/lib
+	cp -RP $(LIBRARY_DIR)/libmbedcrypto.* $(DESTDIR)/lib
 
 	mkdir -p $(DESTDIR)/bin
-	for p in programs/*/* ; do              \
+	for p in $(PROGRAMS_DIR)/*/* ; do              \
 	    if [ -x $$p ] && [ ! -d $$p ] ;     \
 	    then                                \
 	        f=$(PREFIX)`basename $$p` ;     \
@@ -40,12 +56,12 @@
 	done
 
 uninstall:
-	rm -rf $(DESTDIR)/include/mbedtls
+	rm -rf $(DESTDIR)/$(INCLUDE_DIR)/mbedtls
 	rm -f $(DESTDIR)/lib/libmbedtls.*
 	rm -f $(DESTDIR)/lib/libmbedx509.*
 	rm -f $(DESTDIR)/lib/libmbedcrypto.*
 
-	for p in programs/*/* ; do              \
+	for p in $(PROGRAMS_DIR)/*/* ; do              \
 	    if [ -x $$p ] && [ ! -d $$p ] ;     \
 	    then                                \
 	        f=$(PREFIX)`basename $$p` ;     \
@@ -73,24 +89,24 @@
 ifndef WINDOWS
 
 	# If 128-bit keys are configured for CTR_DRBG, display an appropriate warning
-	-scripts/config.pl get MBEDTLS_CTR_DRBG_USE_128_BIT_KEY && ([ $$? -eq 0 ]) && \
+	-scripts/config.pl -f $(CONFIG_FILE) get MBEDTLS_CTR_DRBG_USE_128_BIT_KEY && ([ $$? -eq 0 ]) && \
 	    echo '$(CTR_DRBG_128_BIT_KEY_WARNING)'
 
 	# If NULL Entropy is configured, display an appropriate warning
-	-scripts/config.pl get MBEDTLS_TEST_NULL_ENTROPY && ([ $$? -eq 0 ]) && \
+	-scripts/config.pl -f $(CONFIG_FILE) get MBEDTLS_TEST_NULL_ENTROPY && ([ $$? -eq 0 ]) && \
 	    echo '$(NULL_ENTROPY_WARNING)'
 endif
 
 clean:
-	$(MAKE) -C library clean
-	$(MAKE) -C programs clean
-	$(MAKE) -C tests clean
+	$(MAKE) -C $(LIBRARY_DIR) clean
+	$(MAKE) -C $(PROGRAMS_DIR) clean
+	$(MAKE) -C $(TESTS_DIR) clean
 ifndef WINDOWS
 	find . \( -name \*.gcno -o -name \*.gcda -o -name \*.info \) -exec rm {} +
 endif
 
 check: lib tests
-	$(MAKE) -C tests check
+	$(MAKE) -C $(TESTS_DIR) check
 
 test: check
 
@@ -99,14 +115,14 @@
 # make CFLAGS='--coverage -g3 -O0'
 covtest:
 	$(MAKE) check
-	programs/test/selftest
-	tests/compat.sh
-	tests/ssl-opt.sh
+	$(PROGRAMS_DIR)/test/selftest
+	$(TESTS_DIR)/compat.sh
+	$(TESTS_DIR)/ssl-opt.sh
 
 lcov:
 	rm -rf Coverage
-	lcov --capture --initial --directory library -o files.info
-	lcov --capture --directory library -o tests.info
+	lcov --capture --initial --directory $(LIBRARY_DIR) -o files.info
+	lcov --capture --directory $(LIBRARY_DIR) -o tests.info
 	lcov --add-tracefile files.info --add-tracefile tests.info -o all.info
 	lcov --remove all.info -o final.info '*.h'
 	gendesc tests/Descriptions.txt -o descriptions
@@ -122,7 +138,7 @@
 endif
 
 ## Editor navigation files
-C_SOURCE_FILES = $(wildcard include/*/*.h library/*.[hc] programs/*/*.[hc] tests/suites/*.function)
+C_SOURCE_FILES = $(wildcard $(INCLUDE_DIR)/*/*.h $(LIBRARY_DIR)/*.[hc] $(PROGRAMS_DIR)/*/*.[hc] $(TESTS_DIR)/suites/*.function)
 tags: $(C_SOURCE_FILES)
 	ctags -o $@ $(C_SOURCE_FILES)
 TAGS: $(C_SOURCE_FILES)
diff --git a/library/Makefile b/library/Makefile
index fc67329..4154c6a 100644
--- a/library/Makefile
+++ b/library/Makefile
@@ -5,7 +5,20 @@
 WARNING_CFLAGS ?=  -Wall -W -Wdeclaration-after-statement
 LDFLAGS ?=
 
-LOCAL_CFLAGS = $(WARNING_CFLAGS) -I../include -D_FILE_OFFSET_BITS=64
+# Check test environment. If ../library is available then Mbed TLS is used.
+# Otherwise Mbed OS environment is used.
+DIR_FOR_MBED_TLS_ENV=../library
+ifneq "$(wildcard $(DIR_FOR_MBED_TLS_ENV) )" ""
+	# Set include dirs for Mbed TLS test environment
+	INCLUDE_DIRS=-I../include
+else
+	# Set include dirs for Mbed OS test environment
+	INCLUDE_DIRS=-I../inc
+	CFLAGS += "-DMBEDTLS_CONFIG_FILE=\"mbedtls/test_config.h\""
+endif
+
+LOCAL_CFLAGS = $(WARNING_CFLAGS) $(INCLUDE_DIRS) -D_FILE_OFFSET_BITS=64
+
 LOCAL_LDFLAGS =
 
 ifdef DEBUG
diff --git a/programs/Makefile b/programs/Makefile
index 9b01e45..ea75c1b 100644
--- a/programs/Makefile
+++ b/programs/Makefile
@@ -7,17 +7,30 @@
 WARNING_CXXFLAGS ?= -Wall -W
 LDFLAGS ?=
 
-LOCAL_CFLAGS = $(WARNING_CFLAGS) -I../include -D_FILE_OFFSET_BITS=64
-LOCAL_CXXFLAGS = $(WARNING_CXXFLAGS) -I../include -D_FILE_OFFSET_BITS=64
-LOCAL_LDFLAGS = -L../library 			\
+# Check test environment. If ../library is available then Mbed TLS is used.
+# Otherwise Mbed OS environment is used.
+DIR_FOR_MBED_TLS_ENV=../library
+ifneq "$(wildcard $(DIR_FOR_MBED_TLS_ENV) )" ""
+	LIBRARY_DIR=../library
+	INCLUDE_DIR=-I../include
+else
+	LIBRARY_DIR=../src
+	INCLUDE_DIR=-I../inc
+	CFLAGS += "-DMBEDTLS_CONFIG_FILE=\"mbedtls/test_config.h\""
+endif
+
+LOCAL_CFLAGS = $(WARNING_CFLAGS) $(INCLUDE_DIR) -D_FILE_OFFSET_BITS=64
+
+LOCAL_CXXFLAGS = $(WARNING_CXXFLAGS) $(INCLUDE_DIR) -D_FILE_OFFSET_BITS=64
+LOCAL_LDFLAGS = -L$(LIBRARY_DIR)	\
 		-lmbedtls$(SHARED_SUFFIX)	\
 		-lmbedx509$(SHARED_SUFFIX)	\
 		-lmbedcrypto$(SHARED_SUFFIX)
 
 ifndef SHARED
-DEP=../library/libmbedcrypto.a ../library/libmbedx509.a ../library/libmbedtls.a
+DEP=$(LIBRARY_DIR)/libmbedcrypto.a $(LIBRARY_DIR)/libmbedx509.a $(LIBRARY_DIR)/libmbedtls.a
 else
-DEP=../library/libmbedcrypto.$(DLEXT) ../library/libmbedx509.$(DLEXT) ../library/libmbedtls.$(DLEXT)
+DEP=$(LIBRARY_DIR)/libmbedcrypto.$(DLEXT) $(LIBRARY_DIR)/libmbedx509.$(DLEXT) $(LIBRARY_DIR)/libmbedtls.$(DLEXT)
 endif
 
 ifdef DEBUG
diff --git a/tests/Makefile b/tests/Makefile
index 20a3fe4..dee011f 100644
--- a/tests/Makefile
+++ b/tests/Makefile
@@ -6,8 +6,21 @@
 WARNING_CFLAGS ?= -Wall -W -Wdeclaration-after-statement -Wunused
 LDFLAGS ?=
 
-LOCAL_CFLAGS = $(WARNING_CFLAGS) -I../include -D_FILE_OFFSET_BITS=64
-LOCAL_LDFLAGS = -L../library			\
+# Check test environment. If ../library is available then Mbed TLS is used.
+# Otherwise Mbed OS environment is used.
+DIR_FOR_MBED_TLS_ENV=../library
+ifneq "$(wildcard $(DIR_FOR_MBED_TLS_ENV) )" ""
+	LIBRARY_DIR=../library
+	INCLUDE_DIR=-I../include
+else
+	LIBRARY_DIR=../src
+	INCLUDE_DIR=-I../inc
+	CFLAGS += "-DMBEDTLS_CONFIG_FILE=\"mbedtls/test_config.h\""
+endif
+
+LOCAL_CFLAGS = $(WARNING_CFLAGS) $(INCLUDE_DIR) -D_FILE_OFFSET_BITS=64
+
+LOCAL_LDFLAGS = -L$(LIBRARY_DIR)		\
 		-lmbedtls$(SHARED_SUFFIX)	\
 		-lmbedx509$(SHARED_SUFFIX)	\
 		-lmbedcrypto$(SHARED_SUFFIX)
@@ -18,9 +31,9 @@
 LOCAL_CFLAGS += -D_POSIX_C_SOURCE=200809L
 
 ifndef SHARED
-DEP=../library/libmbedcrypto.a ../library/libmbedx509.a ../library/libmbedtls.a
+DEP=$(LIBRARY_DIR)/libmbedcrypto.a $(LIBRARY_DIR)/libmbedx509.a $(LIBRARY_DIR)/libmbedtls.a
 else
-DEP=../library/libmbedcrypto.$(DLEXT) ../library/libmbedx509.$(DLEXT) ../library/libmbedtls.$(DLEXT)
+DEP=$(LIBRARY_DIR)/libmbedcrypto.$(DLEXT) $(LIBRARY_DIR)/libmbedx509.$(DLEXT) $(LIBRARY_DIR)/libmbedtls.$(DLEXT)
 endif
 
 ifdef DEBUG
@@ -77,7 +90,7 @@
 all: $(BINARIES)
 
 $(DEP):
-	$(MAKE) -C ../library
+	$(MAKE) -C $(LIBRARY_DIR) $(INCLUDE_DIR)
 
 C_FILES := $(addsuffix .c,$(APPS))
 
diff --git a/tests/ssl-opt.sh b/tests/ssl-opt.sh
index 49d2d1f..ecb9a6f 100755
--- a/tests/ssl-opt.sh
+++ b/tests/ssl-opt.sh
@@ -71,8 +71,6 @@
 FAILS=0
 SKIPS=0
 
-CONFIG_H='../include/mbedtls/config.h'
-
 MEMCHECK=0
 FILTER='.*'
 EXCLUDE='^$'
@@ -154,20 +152,6 @@
     SKIP_NEXT="YES"
 }
 
-# skip next test if the flag is not enabled in config.h
-requires_config_enabled() {
-    if grep "^#define $1" $CONFIG_H > /dev/null; then :; else
-        SKIP_NEXT="YES"
-    fi
-}
-
-# skip next test if the flag is enabled in config.h
-requires_config_disabled() {
-    if grep "^#define $1" $CONFIG_H > /dev/null; then
-        SKIP_NEXT="YES"
-    fi
-}
-
 requires_ciphersuite_enabled() {
     if [ -z "$($P_CLI --help | grep "$1")" ]; then
         SKIP_NEXT="YES"
@@ -185,6 +169,19 @@
     ${P_SRV} "query_config=${1}"
 }
 
+# skip next test if the flag is enabled in config.h
+requires_config_disabled() {
+    if get_config_value_or_default $1; then
+        SKIP_NEXT="YES"
+    fi
+}
+
+requires_config_enabled() {
+    if ! get_config_value_or_default $1; then
+        SKIP_NEXT="YES"
+    fi
+}
+
 requires_config_value_at_least() {
     VAL="$( get_config_value_or_default "$1" )"
     if [ -z "$VAL" ]; then
@@ -207,6 +204,17 @@
     fi
 }
 
+requires_config_value_exactly() {
+    VAL=$( get_config_value_or_default "$1" )
+    if [ -z "$VAL" ]; then
+        # Should never happen
+        echo "Mbed TLS configuration $1 is not defined"
+        exit 1
+    elif [ "$VAL" -ne "$2" ]; then
+       SKIP_NEXT="YES"
+    fi
+}
+
 # skip next test if OpenSSL doesn't support FALLBACK_SCSV
 requires_openssl_with_fallback_scsv() {
     if [ -z "${OPENSSL_HAS_FBSCSV:-}" ]; then
@@ -300,9 +308,20 @@
 }
 
 # Calculate the input & output maximum content lengths set in the config
-MAX_CONTENT_LEN=$( ../scripts/config.pl get MBEDTLS_SSL_MAX_CONTENT_LEN || echo "16384")
-MAX_IN_LEN=$( ../scripts/config.pl get MBEDTLS_SSL_IN_CONTENT_LEN || echo "$MAX_CONTENT_LEN")
-MAX_OUT_LEN=$( ../scripts/config.pl get MBEDTLS_SSL_OUT_CONTENT_LEN || echo "$MAX_CONTENT_LEN")
+MAX_CONTENT_LEN="$( get_config_value_or_default MBEDTLS_SSL_MAX_CONTENT_LEN )"
+if [ -z "$MAX_CONTENT_LEN" ]; then
+    MAX_CONTENT_LEN=16384
+fi
+
+MAX_IN_LEN="$( get_config_value_or_default MBEDTLS_SSL_IN_CONTENT_LEN )"
+if [ -z "$MAX_IN_LEN" ]; then
+    MAX_IN_LEN=$MAX_CONTENT_LEN
+fi
+
+MAX_OUT_LEN="$( get_config_value_or_default MBEDTLS_SSL_OUT_CONTENT_LEN )"
+if [ -z "$MAX_OUT_LEN" ]; then
+    MAX_OUT_LEN=$MAX_CONTENT_LEN
+fi
 
 if [ "$MAX_IN_LEN" -lt "$MAX_CONTENT_LEN" ]; then
     MAX_CONTENT_LEN="$MAX_IN_LEN"
@@ -2989,11 +3008,6 @@
 
 # Tests for Max Fragment Length extension
 
-if [ "$MAX_CONTENT_LEN" -lt "4096" ]; then
-    printf "${CONFIG_H} defines MBEDTLS_SSL_MAX_CONTENT_LEN to be less than 4096. Fragment length tests will fail.\n"
-    exit 1
-fi
-
 if [ $MAX_CONTENT_LEN -ne 16384 ]; then
     printf "Using non-default maximum content length $MAX_CONTENT_LEN\n"
 fi
@@ -3026,6 +3040,7 @@
             -s "1 bytes read"
 
 requires_config_enabled MBEDTLS_SSL_MAX_FRAGMENT_LENGTH
+requires_config_value_at_least "MBEDTLS_SSL_MAX_CONTENT_LEN" 4096
 run_test    "Max fragment length, DTLS: enabled, default, larger message" \
             "$P_SRV debug_level=3 dtls=1" \
             "$P_CLI debug_level=3 dtls=1 request_size=$(( $MAX_CONTENT_LEN + 1))" \
@@ -3043,6 +3058,7 @@
 # content length configuration.)
 
 requires_config_disabled MBEDTLS_SSL_MAX_FRAGMENT_LENGTH
+requires_config_value_at_least "MBEDTLS_SSL_MAX_CONTENT_LEN" 16384
 run_test    "Max fragment length: disabled, larger message" \
             "$P_SRV debug_level=3" \
             "$P_CLI debug_level=3 request_size=$(( $MAX_CONTENT_LEN + 1))" \
@@ -3054,6 +3070,7 @@
             -s "1 bytes read"
 
 requires_config_disabled MBEDTLS_SSL_MAX_FRAGMENT_LENGTH
+requires_config_value_at_least "MBEDTLS_SSL_MAX_CONTENT_LEN" 16384
 run_test    "Max fragment length DTLS: disabled, larger message" \
             "$P_SRV debug_level=3 dtls=1" \
             "$P_CLI debug_level=3 dtls=1 request_size=$(( $MAX_CONTENT_LEN + 1))" \
@@ -3063,6 +3080,7 @@
             -c "fragment larger than.*maximum "
 
 requires_config_enabled MBEDTLS_SSL_MAX_FRAGMENT_LENGTH
+requires_config_value_at_least "MBEDTLS_SSL_MAX_CONTENT_LEN" 4096
 run_test    "Max fragment length: used by client" \
             "$P_SRV debug_level=3" \
             "$P_CLI debug_level=3 max_frag_len=4096" \
@@ -3075,6 +3093,7 @@
             -c "found max_fragment_length extension"
 
 requires_config_enabled MBEDTLS_SSL_MAX_FRAGMENT_LENGTH
+requires_config_value_at_least "MBEDTLS_SSL_MAX_CONTENT_LEN" 4096
 run_test    "Max fragment length: used by server" \
             "$P_SRV debug_level=3 max_frag_len=4096" \
             "$P_CLI debug_level=3" \
@@ -3087,6 +3106,7 @@
             -C "found max_fragment_length extension"
 
 requires_config_enabled MBEDTLS_SSL_MAX_FRAGMENT_LENGTH
+requires_config_value_at_least "MBEDTLS_SSL_MAX_CONTENT_LEN" 4096
 requires_gnutls
 run_test    "Max fragment length: gnutls server" \
             "$G_SRV" \
@@ -3097,6 +3117,7 @@
             -c "found max_fragment_length extension"
 
 requires_config_enabled MBEDTLS_SSL_MAX_FRAGMENT_LENGTH
+requires_config_value_at_least "MBEDTLS_SSL_MAX_CONTENT_LEN" 2048
 run_test    "Max fragment length: client, message just fits" \
             "$P_SRV debug_level=3" \
             "$P_CLI debug_level=3 max_frag_len=2048 request_size=2048" \
@@ -3111,6 +3132,7 @@
             -s "2048 bytes read"
 
 requires_config_enabled MBEDTLS_SSL_MAX_FRAGMENT_LENGTH
+requires_config_value_at_least "MBEDTLS_SSL_MAX_CONTENT_LEN" 2048
 run_test    "Max fragment length: client, larger message" \
             "$P_SRV debug_level=3" \
             "$P_CLI debug_level=3 max_frag_len=2048 request_size=2345" \
@@ -3126,6 +3148,7 @@
             -s "297 bytes read"
 
 requires_config_enabled MBEDTLS_SSL_MAX_FRAGMENT_LENGTH
+requires_config_value_at_least "MBEDTLS_SSL_MAX_CONTENT_LEN" 2048
 run_test    "Max fragment length: DTLS client, larger message" \
             "$P_SRV debug_level=3 dtls=1" \
             "$P_CLI debug_level=3 dtls=1 max_frag_len=2048 request_size=2345" \
@@ -3951,21 +3974,10 @@
 # default value (8)
 
 MAX_IM_CA='8'
-MAX_IM_CA_CONFIG=$( ../scripts/config.pl get MBEDTLS_X509_MAX_INTERMEDIATE_CA)
-
-if [ -n "$MAX_IM_CA_CONFIG" ] && [ "$MAX_IM_CA_CONFIG" -ne "$MAX_IM_CA" ]; then
-    printf "The ${CONFIG_H} file contains a value for the configuration of\n"
-    printf "MBEDTLS_X509_MAX_INTERMEDIATE_CA that is different from the script’s\n"
-    printf "test value of ${MAX_IM_CA}. \n"
-    printf "\n"
-    printf "The tests assume this value and if it changes, the tests in this\n"
-    printf "script should also be adjusted.\n"
-    printf "\n"
-
-    exit 1
-fi
+MAX_IM_CA_CONFIG="$( get_config_value_or_default MBEDTLS_X509_MAX_INTERMEDIATE_CA )"
 
 requires_full_size_output_buffer
+requires_config_value_exactly "MBEDTLS_X509_MAX_INTERMEDIATE_CA" 8
 run_test    "Authentication: server max_int chain, client default" \
             "$P_SRV crt_file=data_files/dir-maxpath/c09.pem \
                     key_file=data_files/dir-maxpath/09.key" \
@@ -3974,6 +3986,7 @@
             -C "X509 - A fatal error occurred"
 
 requires_full_size_output_buffer
+requires_config_value_exactly "MBEDTLS_X509_MAX_INTERMEDIATE_CA" 8
 run_test    "Authentication: server max_int+1 chain, client default" \
             "$P_SRV crt_file=data_files/dir-maxpath/c10.pem \
                     key_file=data_files/dir-maxpath/10.key" \
@@ -3982,6 +3995,7 @@
             -c "X509 - A fatal error occurred"
 
 requires_full_size_output_buffer
+requires_config_value_exactly "MBEDTLS_X509_MAX_INTERMEDIATE_CA" 8
 run_test    "Authentication: server max_int+1 chain, client optional" \
             "$P_SRV crt_file=data_files/dir-maxpath/c10.pem \
                     key_file=data_files/dir-maxpath/10.key" \
@@ -3991,6 +4005,7 @@
             -c "X509 - A fatal error occurred"
 
 requires_full_size_output_buffer
+requires_config_value_exactly "MBEDTLS_X509_MAX_INTERMEDIATE_CA" 8
 run_test    "Authentication: server max_int+1 chain, client none" \
             "$P_SRV crt_file=data_files/dir-maxpath/c10.pem \
                     key_file=data_files/dir-maxpath/10.key" \